What maintenance do you do on your weapons besides cleaning? Do you gauge them, barrel, CHS?
Low volume guns? Nothing but a wipe down and lubing after use as well as periodic spot check for rust or dried off parts that always need to stay lubed.
Higher volume guns, depends really and on which type. After each match or training course I wipe down, degrease, inspect, and bore scope for any gas port erosions. On the AR's there's nothing that I don't already have in spades to easily replace anything. Like a broken extractor. That's happened. Same for worn down gas seals failing the BCG dropping or not on it's own test while standing it up on it's bolt head.
Sig will replace almost everything for $89 per pistol and their CS is super fast. Free shipping 2 day Fedex both ways so it's cheaper for me to do it this way and never have to worry about which spare parts to have on hand for the P226R, P320 Compact Carry Nitron 45 ACP, P320 Compact Carry 9x19, or my newer 365X Macro.
Glock has a factory armorer at each GSSF match and they will replace almost anything for free. But since I use them exclusively I also do keep things on hand. If something breaks I put it down and get one of my backups while their armorer takes a look and replaces things. Only happened once but it's nice to know that they do it on call while there no questions asked.
HK is awesome about their warranty too and will 3 day it on their dime pretty much anything I ask for at no charge. Only had to replace a worn down guide rod/spring, and had to send in a VP9 to have it's slide looked at that was replaced as well as the most of the frame's internals.
For my 1911's I am the test shooter for Roger's Precision so he does the tune ups, custom work if needed, and inspections for free on my Staccato P, Colt model 70 Competition, SA Loaded, and SA Operator.
I generally don't gauge my barrels and only replace if accuracy starts to degrade so I'll deep clean, shoot 60 rounds to let the copper fouling recover any imperfections, shoot for group size and if it's still bad then I will replace. If I replace I head space everything and leave nothing to chance.
Right now I am still learning the X95 Tavor and will have an armorer's class this coming May, so I will be able to ask and be educated on things as well as learning about their CS and common parts to have on hand for quick repairs.
