Its pretty safe to buy a mediastation as its a PC with some extra peripherals and anyone with extensive knowledge of PC's can diagnose it.
Most parts are COTS (Custom of the shelf)and you can replace them yourself, some parts are custome made by lionstracs and need to be ordered by lionstracs.
So actually its easier to diagnose faults in mediastation. If you want to use the mediastation for gigging, make sure you have 2 harddisks you can use for swapping, and do not experiment on the HD wtih your stable version.
This i base on my extended knowledge of computer hardware. I have had no handson experience with mediastation however.