This seems very very weird to me. Yes I know that stainless is stain"less" but for one to actually rust to the point of pitting in Ohio would take something bordering on freakish. I have 2 stainless Ruger handguns and a couple SS rifles that see only modest amounts of care and nothing special in the way of storage, never seen a bit of rust on them. Had some blued guns that had a hard summer a few years ago with lot's of heat and humidty but the SS guns were unphased. Don't get me wrong I've seen rust on stainless guns stored in bad conditions for a period of time but even then there wasn't any pitting and it cleaned up with some steel wool never to reappear.
Also keep in mind what may look like pitting may just be unfinished areas from the casting. IME, Ruger doesn't do too much finish work under their grip panels.
Grips could be a cause. Not from the sweet of your hands but from something left behind at the factory. Don't ask me what, I've never heard of anyone with this issue. Maybe a bad casting from Ruger?