balanceman

Thank's very much folks. Getting your info has given me confidence to investigate further, make a more reasoned diagnosis and carry out repair /change the seals if necessary. Will report back on my progress. Probably asking if anyone knows how to re-assemble it. :-)

Great, thanks for the quick answer and pointer. Don't seem to have lost water from the rad. Which makes me think that it could be river water after all. I have taken my bike for a couple of healthy swims recently.

Hello knowledgeable ones. If the gear oil is coming out grey and milky after about 6 hours use is that normal. Someone told me it could be river water that's been sucked in, or head gasket or water pump seals. I've come late to trials - the riding is tricky but the maintenance seems a minefield.