Volvo XC70 gearbox warning caption

I experienced some jolts in my XC70's gear changes, mainly when changing from Neutral to Drive. It wouldn't change straight away and then jolt into gear making the car jump forwards. I took it to my local Volvo who said there wasn't a problem and said it was because the car was still recognising my driving style. I wasn't sure this was true, but didn't take any action to see if it would sort itself out. About a month later, the car was still the same and a caption came up saying 'Transmission Fault'. I took it to a friend's garage who plugged it into his diagnostics kit, which said several different errors such as 'Clutch posistion error' and 'clutch sensor fault'. It sounded expensive, but my mechanic suggested changing the gearbox oil, even though it wasn't due. The oil was changed and the problems all dissappeared. There may have been something blocking a sensor, and the oil change removed whatever had caused the problem. Although the £75 oil change seemed expensive, Volvo would have charged at least ten times that to change all the various components that the diagnostics had faulted.