Personally I'd recommend (they are brilliant)
Steve / Paul
Hughberry Vehicle Services
Unit 3 The Old Quarry
Springwell Lane
Rickmansworth
Herts, WD3 8UX
Loads of people from SIDC go there (for rebuilds/servicing) etc etc.
Do a search for them in the General forums.
http://forums.sidc.co.uk/lofiversion/index.php?t118043.html