I've not had any dealings with Supreme other than a unsuccessful search in their "chandlery" some years ago for some gear oil !!
Having tried to find a good service agent for both my own and our dive club boats, I think we have found a gem in :
M J Marine Services
New Holland DN19 7RE
Tel: 01469 532231
Fax: 01468 532231
Give Mark a call if you need anything in the future. He is a genuine guy with a lot of knowledge and pride in his work ......... and has a large lake on hand for engine testing
Mention my name ......... he'll probably add 10%