cheers the top cover gasket is fitted correctly and the hole is clear inside the top cover
Would need to find more info on the hole in the head with the breather valve as bilgediver said.
if the older style engines had a pipe to the air cleaner where did it suck from (a fitting on the top cover??) this may be an option to let me use the boat this summer and remove the cylinder head this winter if the breather valve is blocked.