Nice to see so many alternative ideas. Bit like a design team think-tank. I appreciate the view I should ride the GF more often, but I have other bikes, some classic cars and a few other interests that conspire to reduce my riding time. The GF usually gets a ride around once a week (in decent weather) so the oil-in-sump aggravation is one that's really getting on my wick. As I've posted elsewhere, both my BSA B31 and M21 wet-sump, but to a far lesser degree. Also, one can ride them to clear the sump if necessary, whereas the GF belches out smoke and pours oil out of the breather if I try that. And, as stated a couple of posts ago, they can easily be fixed anyway by giving the ball a tap with a punch. The A10 requires a full engine strip to do that. Madness. No wonder BSA woke up and modified the system for the A65.
The valve in oil line approach is risky and if using a key requires a bit of re-wiring too. What I'm looking for is the easiest / cheapest / most reliable way to solve the issue and it seems to me that converting to the A65 type set-up is the answer. Of course, the ideal time to do that is when an engine is stripped but, at the time I had it down, I was unaware of this design weakness. When I get around to pulling the cover and pump, if I find the conversion I propose feasible, I intend using an air blast through the pressure release valve orifice to help clear swarf and to drill slowly with coarse feed, thereby minimising small chip production. A second air gun with small tube placed at the rear of the hole should guarantee no swarf gets where it shouldn't.
Best wishes to everyone for 2019.