Finally solved the wet sumping issue..
Short version - change to mineral oil (V twin specifiuc of course)
Long version - bought the car from BHM just serviced and for the first year I had no leak at all. Did the first servioce after a year and switched to Motul V twin fully synthetic and the leak started. If I was leaving the car parked for more than a week I had to drain the oil. Lived with this for two years and finally twigged. Chnaged back to mineral oil and problem solved !
My engine suffers quite badly from wet-sumping if left idle for more than a couple of days. Therefore, I was excited to try switching to mineral oil to see if it would resolve the situation. In a nutshell, I did and it didn't. No perceivable change in wet-sumping behaviour with mineral oil over synthetic as far as I can tell. The only advantage I now have is that I can see when I've wet-sumped due to my new clear vent line.
