The only thing you ever really have to replace to keep an 1100 running are the gas seals. Basically, they're just rubber o-rings, and they cost about $2 (maybe). I replace mine once a year whether they need it or not. Unless it was just a lemon from the factory (doubtful), that should be about all you need to do besides cleaning and oiling it.
I have three 1100 12ga shotguns. One from 1963, one from 1978 and one from 2008. All of them run like tops with little other than regular cleaning.