I bought one of these MX900 from ebay. The volume down button was working intermittently. Complete disassembly (also took out the clear plastic used for light distribution) and cleaning with 90% isopropyl (rubbing alcohol) removed a little residue and fixed my problem too!

I would have tried calling URC, but I assumed they'd never talk to me since I'm not a dealer. I'm not complaining though. I paid $90 for the remote and a MRF-350 that appears to be still sealed. I'm clueless why anyone would pay a dealer $499 or whatever for it.

Overall, I think the remote software is very easy to use. I was able to do a complete install with an MSC-400 and an MX-900 in just a few hours and I've never done it before.