Oil/water sludge on end of V4 plug

[hotrods65]

G'day all,

New to this forum. Was just changing the spark plugs in my yamaha 130V4 outboards and noticed a very small amount of oil sludge on the end of one of the top spark plugs. I am assuming I have a head gasket that is hopefully just started to leak, will do a compression test later today. Could anything else cause this ?, engine was running fine when last used and there is no water on the fuel/water separator bulb.

Any advice appreciated.

Cheers

Hotrods65

[boats.net]

Check for low compression, check head gasket, heads for corrosion and may need to check inner exhaust plate for corrosion.