I have a Mossberg 500A that I bought a few years ago strictly for HD. Its the SG Big-5 always has on sale (20 inch barrel). Anyway, I haven't done anything to it except shoot it every few months for piece of mind. Are there any parts on there that should be upgraded to make sure it goes boom each and every time? I'm not talking about tacticool parts either. Is there some plastic or metal on there that are prone to early wear and should be replaced with something after-market? I realize that this SG is not the best out there but it was all I could afford at the time and I want to keep it functional for years to come. So is this an "if it ain't broke, don't fix it" situation or are there good upgrades?