What is the difference between the M9 and the M9-P?
Not much difference. There is nothing different mechanically, exact same internal workings. The M9-P has sapphire glass covering the rear viewing screen, more scratch resistant. The only other differences I know of are elimination of the red dot and "Leica" on the front. "Leica" is inscribed on the top plate.
I had an M9-P for one week when the faux leather started lifting at the rear screen. So I returned it, and bought an M9. Which after a longer time, the same thing happened. I sent the camera to [www camera leather com] (not allowed to include other web sites, so join camera and leather into one word and put a period after www and before com) and had real leather installed. Zero problems since then. Well, except for the sensor cracking just before a vacation to the Galapagos.