Kevin- congratulations on your purchase. I have one of these lenses (bought from Raid several years ago!) and I absolutely love it. The M3 is absolutely the best M series Leica for fast 50's (and almost any other lens, IMO). The camera balances very nicely with this lens, and the finder and RF are both a really good match with it- better than the .72 finder Leicas would be.
Don't worry about the finder de-cemeting. Despite what you've read, I'm sure it's a relatively rare problem. For all the ones that have come un-glued, there must be a few hundred still working perfectly. Get a clean one and don't worry about it. I have used a pair of M3's pretty hard for the past ten years, and they still look the same through the front- a little crazing, but no problems, and more importantly, no change. I wouldn't let the possibility of a bad finder deter me from an M3; or, if I did, I'd probably have to rule out the M2, too. Most M2's are nearly as old as many M3's, and they use the same Canadian balsam, so the finder is no more or less likely to de-cement.
Finally, if it does happen, they can be fixed- although you could probably replace it for less money. IF you had one de-cement, I bet you'd never have it happen to two cameras...
