If your MX has never had it's seals replaced, it's a good bet that it will need new ones. The seals are along the rear of the camera body, where the door seats against it. There's a channel running along the top & bottom edge of the rear camera body that the seals reside in. Also at the door hinge area. Chances are the mirror bumper foam will need replacing. If the seals & bumper are frayed, gummy, or just not there anymore, then you'll need to replace them.
Jon Goodman makes DIY seal kits with a tool & complete instructions for $10 shipped. It's not that hard, if you take your time & follow the instructions. I've replaced seals using the kit on an ME & Spotmatic with very little trouble, having never done it before. I have no idea what a camera shop would charge, but really, it's not that difficult. I'll see if I can dig up Jon's email & will check back. Congrats on your MX
edit: Here's the email for Jon @ Interslice:
jgood21967@aol.com
Great guy to do business with! (no affiliation)
Last edited by paulh; 09-07-2012 at 12:18 PM.