best advice I can give is always check your manual, get the part number of what's broken, and type it into (any online hobby shop/ebay).
For example, the diff in a 2wd slash (don't need to say center, there is only one diff) is 2388X, typing this into towerhobbies yields this:
http://www3.towerhobbies.com/cgi-bin...388x&search=Go
Of course you can save money by figuring out what is exactly wrong with it.
2 years and I've never had a problem with the diff, even in snow. I sheared off a Castle motor shaft before I damaged the diff.
