I've got an old Pentax ME Super which I haven't used for around 4 years. However, it has always had an intermittent problem in that it winds on twice meaning that i waste half my film. Can anyone recommend a good place to take it to? Perhaps I am better off just buying a new body??

Try calling these guys http://www.hlehmann.co.uk/ might be able to help :)

Harrison Cameras on London Rd may be worth a try.

Might be worth having a word with http://www.lutoncameras.co.uk/ Not used them myself but they seem to have a good reputation in the Olympus community; they do Pentax too.
Theres a link on the left hand side to get a repair estimate without sending the camera off to them.