I have a Noriel (Sq4 in a wideline featherbed frame) with an AMC gearbox. The gearbox oil seems to be leaking in the vicinity of the sprocket. I have replaced the sleeve gear bearing oil seal which seems to have reduced the flow by about half. I am sure the oil is coming out of the gearbox (as opposed to the primary chaincase) as the oil level in the gearbox is visibly lower even after a short ride. I can't see any other oil seals in the vicinity of the main shaft or sleeve shaft that could be at fault. Any suggestions?