The "newest" pistols were built in 1945 but as mentioned may have been rebuilt a number of times. The pistols at training units got the most use - some kept up well, others not, depending on the unit. Most officers and some Armor crewmen qualified with a .45.
Each line unit in the Army has a "TO&E" - Table of Organization and Equipment. This says, for example, that the Battalion Commander is issued a .45. while his driver might be issued an M16. I was in a Cav Squadron and tank drivers were issued M3A1's - "Greaseguns."
As a Cav Platoon Leader, I was technically issued an M16, and that's what I qualified with. Am Armore Platoon Leader was issued a .45. But because of paymaster and Border Camp duties, I was eventually issued a .45 as well. I don't remember anything about it - we'd do function checks and if something was busted, it got fixed as parts wee abundant. I bought my own .45 so that if the flag dropped I would have a weapon that might actually hit something I pointed it at.
The .45 round is relatively low velocity and apparently relatively low pressure as well. Magazines have tested new M1911 clones for 10,000 rounds, with few malfunctions. One magazine tested a SIG P220 (a modern, double-action .45 very popular in Ft. Bragg, NC) for 10,000 rapid fire - as fast as they could shoot it, subject to some cleaning. They broke a part (that SIG recommends replacing every 5,000 rounds) and after cleaning it shot tighter groups (1.9" at 25 yards) than it did when new (2.1"). So it seems that .45 ACP pistols of all types last a long time. I've heard of range rental SIGs with 30,000 rounds through them.