Think I am sorted now. Took the calliper to a friend’s workshop yesterday and we managed to recess the pistons and then replace the seals successfully. There was a lot of white rust behind the seals and the calliper needed a lot of cleaning so that may have been the problem. They could have been in there since 1997. He is very experienced engineer and he thought it was strange that the pistons didn’t recess easily, so the problem may come back. Have rebuilt the rear brake and bled it, just need a test ride now to try it out. Thanks again for all your advice and suggestions. Need to look now to see why the temperature gauge isn’t working!