How far into warranty?...how old is it?...Don't skimp on a service coz it's expensive. They are in need of TLC.
I (and lots off the board from around east Midlands and N/S yorkshire) go to cornerspeed. servicing is second to none and although independent servicing undercuts the main dealers.
I nullified my warranty to take it to cornerspeed... well worth it tho' IMHO
