They could do you the SMG up-date
(if not already) for £60 and see if that helps.
£250 to strip it down, how much to put it back together again?
There's obviously going to be something wrong, even if it's the flux capacitor?
A lot will depend on mileage, under 60K and it shouldn't be 'wear & tear' over and it could be.
The only person that knew anything about the CSL's little idiosyncrasies at Elms was Gareth and he now works for Bartlett - draw your own conclusion.