Also a good idea to make sure any air openings on the generator head have expanded metal mesh over them so the mice cannot enter the case. Look ALL over the gen head. The ST-5 I have has grates over the side air vents, but the ones underneath that you cannot easilly see, are wide open...
Lack of use is probably the biggest killer of backup generator engines. You buy the thing from the box store in preparation for that big storm, use it a few hours, then it sets for years in the back of the garage. Next big storm hits, power goes out, and you think cool, I got a gennie. Well first thing goes wrong when you pull it out is it won't start. Once you get the bad gas out and the plug unfouled, you get it online and strut back inside to watch the ballgame laughing at your neighbors setting in the dark. This goes on for about an hour till the corroded main and rod bearings finally eat themselvs and stuff the rod end thru the case. This on a new generator with only a few hours on it... Then of course your neighbors start laughing at you from their dark homes...
Lawnmowers have the same basic engines. They last so long because they have the benefit of typically being run at least half the year...