Replying to my own post it may help others who have oil getting into the clutch to check the fit of the big PD21 seal that runs on the back of the clutch sprocket. Despite fitting a new seal I was still getting oil through after not too many miles. I eventually found that the seal was a poor fit in the primary case and once everything had warmed up the seal was just loose in the case and gradually letting oil through. The cure was to bore the hole a little oversize and press in an alloy sleeve that could then be machined to give the correct fit for the seal........ I then fitted the standard Vincent clutch and have to say that it is a much better unit. It would unfair to say that I had no problems with the standard clutch. One problem was an inadequate oil seal/seals and also having to gain some understanding as to how the clutch works so that I could be adjusted properly. The oil problem seal problem manifested itself on a visit to Dolgellau in Wales but I was still able to make the 130 mile trip home using just the primary clutch, albeit at a reduced speed of 50 - 55 mph. ............