As you live in the UK, there is a repair service offered by a company called the Camera Workshop based close to Milton Keynes. Just google the name to get the telephone number and address. The owner of the company was astute enough to buy up all the available spares for Minolta's when they sold out to Sony. If there is anyone who can sort it out, he will be able to. I had my XM given a general service together with a small repair to the shutter speed dial and the turn round time was about 8 days. The cost for a good clean, service and the repair was about £79.
As an afternote, the XM has possibly the quietest shutter ever on a SLR and is a dream to use.