I can only speak from a couple of months owning a AA S400. Basically all that's needed is to keep it clean. Worth dropping the action out of the stock ASAP if it has been wet to ensure all the water is wiped off and the surface oiled for storage. Some like to clean the barrel regularly, other don't.

I did have occasion to clean dried grease off the hammer rail, so cleaned and re-lubed the trigger unit whilst I had it off the gun.

Certainly AA and probably most manufacturers state that the air cylinder should be inspected at least annually and they will condemn it once it's 10 years old. They also suggest that the rifle should be serviced annually. Since servicing entails stripping cleaning and replacing all the seals,I suspect that most owners ignore this until a problem arises. My own gun was manufactured in 2006 and was given to me having had little use, maybe 200 pellets. It's working fine, producing the correct power level and won't be touched until a problem arises.

Rob.