Unfazed - Thanks for the info you learn something every day
Lez72 - I have drained the oil and changed the filter but with the plug out oil was still leaking out. The plugs location is slightly above the window but obviously as unfazed says an oil gallery without draining all oil a minimal loss seems unavoidable less so if your quick
Parts ordered from dealer
Yamaha plug Part No/ 36Y151890000 £12.04
Yamaha O ring Part No/ 932101662900 £1.81
Many thanks everyone