My car is a 2007 Volvo V70 diesel automatic with 54,000 miles. It is serviced by the Volvo dealer as required. When towing a caravan (but only then) I get a warning saying 'Transmission service required' after travelling 30 - 40 miles. I advised the dealer who carried out a check at a cost of £29. He recommended that the transmission oil should be changed (at a cost of £250) but cannot guarantee that this will solve the problem. There is also a solenoid, which he says may be sticking. I would appreciate your opinion on whether the oil change is likely to clear the problem and whether his charges seem reasonable?