Well, for one thing, there are different types of magazine
failures.
Pistol magazines are
assemblies. Assemblies can experience wear & tear on their component parts, as well as being subject to unintended damage, unexpected parts failure, etc.
Magazines, being assemblies, can be inspected and maintained, and either repaired or replaced, depending on the nature of the problem encountered.
Heavy training use of magazines ... (dropping them onto hard surfaces, contamination by excessive fouling, dirt, debris or being submerged, etc) ... may require periodic inspection & cleaning, or even replacement (if damage occurs which can't be corrected by simple parts replacement, like when the mag body is damaged).
No surprises, right?
I've experienced and observed (as an instructor & armorer) pistol stoppages and other failures-to-feed caused by
magazine problems.
Sometimes it required
cleaning of the mags.
Sometimes
replacement of a
part (spring, follower, butt plate, insert).
Sometimes it required
replacement of the
mag (body out-of-spec, damaged, etc).
Different gun companies who provide armorer training may differ a little in their recommendations to their LE/gov clients when it comes to recommending periodic mag inspections, servicing and maintenance.
The environmental & operational conditions in which the equipment is used are always going to remain factors to consider, too. Indoor or outdoor, desert, around fresh or ocean water, windy conditions (blowing grit), dramatic temperature fluctuations, etc.
I remember when the SIG instructor said that a pistol isn't clean unless the magazines are also clean.
In my last (4th) Glock armorer recert, it was said that complete magazine disassembly wasn't recommended as a routine cleaning practice,
unless necessary, and that excessive disassembly & reassembly might cause unnecessary & accelerated wear on the plastic mag body detents. Not emphasized in that manner in my previous classes. Guess they may have seen something happening among some segment of their LE customer base, maybe? (Armorer warnings and recommendations are often the result of something observed & seen, or reported by users, somewhere.)
One thing they all seem to agree upon is that mags out to be dry, mostly meaning not being contaminated by the users by leaving solvents, CLP's or lubricants inside the assembled mags. It can act as a magnet for fouling, dust, dirt & debris, compromising the intended free movement of the ammo load under normal use.
The "spring replacement" subject often comes up in internet gun forums, but never arrives at any sort of definitive conclusion. Not one that pleases everyone, at any rate. Gun company recommendations can vary a bit, too.
Springs are pretty cheap parts. It's not like each and every one is a carefully hand-crafted bit of equipment, right? I spoke with one spring company who said they may ship some springs in 10K count cartons to gun companies and mag vendors. Think each one is individually tested prior to shipping?
I've seen little used mag springs that have only been left loaded in LE guns, and only subjected to live-fire for quals 1-4 times a year, fail to exert sufficient tension in as little as 3-4 years.
I've seen others keep working in heavily used range mags for years at a time.
I've seen them 'go soft', or take on some weird bend or twist, too.
I've seen mags made for larger pistols start to exhibit signs of weakened springs when used in smaller pistols (faster cycling slides of reduced slide mass), but continue to work, longer, as intended in the larger guns.
I've seen some in the hands of private citizens and LE alike, in guns that are often carried but seldom fired for practice (another topic, for another time), which worked for years, but then one day they just stopped providing enough tension for normal feeding and functioning. Usually on the qual range I was working. Oops. Good thing it usually happens on a range, right? Until it
doesn't only happen on a range.
One guy with whom I working on a range one day, who carried a personally owned G22, had his G22 exhibit repeated feeding failures due to obviously weakened mag springs. He told me (when asked) that he'd never replaced (nor had an agency armorer replace) his mag springs in the 10 years he'd been carrying that gun, but that he only shot it maybe once a year for quals at his agency. He also pretty much shrugged and told me that if his springs were weakened, it probably explained why his G22 had repeatedly experienced feeding stoppages when he'd been trying to shoot an attacking pit bull in recent weeks.
Guess what I recommended?
Personally, I don't take mags for granted. I do the basic armorer bench checks for functioning (checking for slide lock running the slide briskly with an empty mag, checking follower lift & function, freedom of appropriate movement & fit when the mag was inserted & released, etc). If a mag hits the ground (especially when dropped on our outdoor sand-covered range), it gets cleaned and inspected.
I
prefer to occasionally set aside some mags as dedicated range mags, but then as a firearms instructor I tend to do a lot more shooting than the average cop or private citizen. It lets me run, observe and continually evaluate mags under heavy-use conditions, up to and including adverse and abusive conditions, to see how they work ... without risking compromising any reliability of my regular carry mags.
I still periodically run my carry mags, though, to continue to confirm normal functioning.
If a range mag ever requires replacement (and they have), I'll generally rotate a carry mag over to a range/training mag role, and put a new mag into service for the carry role ... after range confirmation of expected functioning, which usually includes firing 25-50 rounds of whatever carry rounds I'm presently using.
Pistols magazines can be at the very heart of expected optimal feeding & functioning of pistols. When it comes to a dedicated service/carry weapon (not some leisure range sporting/target pistol), I like to err on the conservative side of things.
FWIW, when some folks (both cops and private citizens) complain about thinking of having to drop the pistol mags onto the ground in a real shooting situation (which is a good reason to develop the unconscious ability to do it, as a tactical skillset), I remind them that spent & dropped mags aren't going to be an immediate 'problem' for them ... since they'll most likely end up being taken into evidence and held, along with their weapon.
Are you shooting hundreds of thousands of rounds annually? Waste of money in my opinion. A new, refurbished magazine can fail just as easily as a new one.