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 oilo and problem solved !
