Wet sumping never used be a problem, but I am hearing of it more and more.
I have recently had a case of wet sumping due to the valve (item 10 in the above diagram) sticking due to a varnish like build up. In this case the bike had been sitting for a long time.
I used some 1000 wet and dry to clean the valve body up and this fixed the problem.
The only other time I have seen wet sumping, was when a bit of gasket lodged under the valve. I don't know how it got past the inlet screen, but it was the problem.
The three collars are necessary to hold the o-rings in place, otherwise they could actually partially block the opening.
At a vintage rally I was told that a person had problems because of a damaged rubber seat (item 11), and as mentioned these are hard to find. The part number is 15166-300-000 and Western Hills have a price of $2.72, but they do not seem to have any stock.
Neither CMS or David Silver Spares have any available
If anyone can find these rubber valves it would help us, as a lot of these rubber components are now over thirty years old and surely will not survive much longer.
Regds Clyde