If you have the car`s "Audio Guide" then the Serial Number ( + code) might be in there
( Beginning with M * * * * * * )
If not , then the radio will have to be extracted from the dashboard.
If the garage reckons the retaining clips are damaged, then the chances are they have been bent out of shape.
With a little patience then you might be able to "jiggle" each individual clip by using one of the methods mentioned here :
www.tinyurl.com/4ydhop
Good Luck !
RegWorts, July 2008