Spent a couple hours on teardown and cleanup this morning. Only a single rivet is broken and it cleaned up really nicely.
The rivets towards the bottom are broken (not uncommon for Model Ms), so a bolt mod is in order, which should improve key feel. All keys are functional however.
Even though I got mine a while back, I have yet to check for broken rivets. I'd be more of less nervous to do my first bolt mod on this sucker, considering they're pretty rare and certainly not cheap. I'm assuming broken rivets are pretty common.
I don't blame you for not wanting your first bolt mod to be an SSK. Bolt mods aren't terribly difficult, but there are some things I didn't fully understand until I actually went through the process (I've done one full bolt mod and one partial). The main two recommendations I'd make are 1) to make sure you drill straight holes (use some sort of brace, a good bit, and a steady hand) and 2) drill the holes before you break the sandwich apart because the metal holes don't line up quite how you'd think; also, that way, the barrel plate still has the support of the metal back plate when you're drilling.
On my first one, I broke everything apart before drilling. It was harder to get the holes aligned properly this way, and it was harder to brace the barrel plate without the metal back plate on it (it's actually a pretty flimsy piece of plastic when it's not riveted to a piece of metal).
That said, don't mutilate a Model M unless it actually NEEDS a bolt mod. If it feels nice to type on, and all the keys are functional, it doesn't need it. Weak clicks in the numpad, nav cluster, or modifier keys are the usual signs of needing one in my limited experience.