A Yamaha dealer I have always found very helpful is Robin Curnow – Outboard Motor Servicing based at Falmouth - seem to keep a lot of parts for older motors and always helpful if you call them.
That might be the answer Coveman - particularly if I was prepared to be patient.
The outboard came home to Northumberland with me following lift out in Late October - but the boat and tender are in Falmouth.
I'll try Robin Curnow tomorrow