I keep coming across threads about some guy who owns a blued Service-Six with some rust spots. That you?
It's your gun. Do as you will.
I'm another long time owner/shooter who has often regretted getting rid of any number of guns when I was younger. Among them were a number of Security & Speed-Sixes, more than half of which were blued. I also let a blued 4 5/8" Blackhawk chambered in .44 Magnum slip through my hands (apparently they only .44 Blackhawks for a short while), and it was only because the cylinder face had a slightly rough finish and some uneven blueing.
Boy, do I wish I wish I still owned those blued Rugers.
My first DA revolver was an old blued Colt that was more bare metal than a hint of remaining bluing. I kept the gun clean and wiped down (not slathered with oil, though). I did a lot of shooting with it, nasty finish and all. Cleaned off any rust as it appeared.
I had a friend whose touch and sweat could rust a gun literally overnight, unless he wiped down the exposed metal of the grip and any part of the cylinder he'd touched each time he handled it (and sometimes forgot to wipe it off after handling
). His older S&W .38 showed how much he'd handled it. Fired and ran just fine, for many years, though.
When I carried an issued revolver on-duty as a young cop, a lot of the other older guys still carried their blued Pythons or blued S&W's. I noticed a lot of them kept towels in their lockers which they used to wipe down their guns at the end of each shift, and then left the guns sitting on the towels on the top shelves of their lockers. Rainy days & nights could be rough on blued revolvers if left hanging in leather holsters in lockers, or even if removed from holsters but not wiped down to remove the moisture.
I saw my fair share of blued Pythons and S&W's with some "rust spots" and finish wear/discoloration from daily carry in leather rigs. Nobody thought it unusual to have to keep on top of stopping rust on their blued guns (but you cloud always tell the guys who were less attentive).
I remember when using some type of wax was discussed by some guys. Never tried it myself, as I just wiped down my guns ... and learned to use holsters that were either made of better leather than cheap, thin suede "pockets", or occasionally were lined, to help keep excessive amounts of sweat off my guns. I let the inside-the-waistband revolver holsters air out after sweaty days, too (back when I didn't mind carrying a medium or large framed revolver IWB).
Now, the only Ruger DA's I still own are all stainless, one of which is an older Service-Six 4" Heavy barrel.
I do miss those older blued Security & Speed-Sixes, though. Wish I'd never let them slip through my hands.
I still think of that .44 Blackhawk any time I take my blued 4 5/8" Blackhawk .45 Convertible out of the safe for some range time, too.
I never had the urge to buy a GP100, although I did pick up a SP101DAO and a Redhawk 5 1/2" .44 Magnum. The SP101 required a correction to resolve a cylinder stoppage problem when the gun got heated from fast shooting (revolver armorer at work helped identify the problem and suggest the minor repair), and the Redhawk had a problem (NIB) which Ruger corrected by replacing the trigger housing, hammer and cylinder. Still got both guns, and they're fine revolvers for 'working guns'.
FWIW, even stainless steel can still rust, if neglected.
If you don't like that blue Service-Six, there's probably going to be someone else who considers it a "find" and will be more than happy to use & shoot it, regardless of minor rust spots & finish wear.
Your choice to make.
Luck to you.