Gear boxes on early models seemed to be an issue, as said, power steering pumps as said, sunroofs warp and wont open/close properly and may leak.

They do seem to be a problematic little car, but that said, my sister has a 51 plate cat C one and it didn't really cause her much trouble. My other sister has a 55 plate and the steering pump went but not much else really. I guess just buy the best you can rather than the newest is the key.

http://www.minitorque.com/forum/forum.php

above site it friendly and should help with buyers guides or problems to watch out for.