Just in case anyone is thinking “I’ll get an after-market automatic anti wet sump valve”, when I was researching this topic for my Norton it seemed that only the Velocette device had a good track record.
Other than that there’s a long trail of broken engines caused by air locks downstream of the check valve and immediately in front of the oil pump (which they are not good at dealing with) and so the valve fails to open up on pump suction as it should.
So for me it’s either fit a manual valve with a BIG sign or run your engine regularly.
