Dominator 99 oil leak

The engine breather commonly spews oil out in the same area ,usually when the pistons are not fully run in , or after starting . The sliding seal over the gearbox shaft  wears and is often damaged . The alternator cable grommet is another weak point.The case is often overfilled which makes all the problem areas much worse . The correct level is somewhat BELOW the "Level plug ) hole . If all is correct I find I dont need to top up at all as oil still finds its way into the case (and out!) from the Engine mainshaft seal. Usually  I need to put the bike on its side stand to drain a  bit out   to keep the level right. Chains need very little oil, as long as they are not dry they survive well.

Agreed. Chains in a case, if boiled in Putoline don't need oil at all. The clutch seems to work happily enough without oil, too. I extended the breather pipe to the bottom of the back mudguard, and respectfully suggest that all Dommi Nortons will wet-sump so fit a valve with incorporated magneto earthing cut-out switch, which solves the problem. No more mess on the floor.

i now have 3 tin chaincases to worry about. Interestingly they are all in a decent shape and none leak oil if left stationary . The drips only  appear during or just after a run.This says that the problem is not really the rubber seal. More likely the gearbox shaft area or cable exit.

One of the weaknesses of the Dominator is the crankshaft oil seal. Lots of owners just assume that it will be up to doing a good job year after year. The reality being that, just like tyres, these seals deteriorate with age and usage.  When they are worn, dodgy oil seals will allow oil from the crankcase to enter the primary chaincases. Especially if the engine is started after a long lay-off and has wet-sumped.......even a small amount.  The air inside the chaincases then becomes pressurised and pushes the excess oil (vapour) towards any gaps. These generally being the holes for wiring leads, the gearbox mainshaft and the footrest tube.  This is asssuming that the main chaincase seal is not already adding to the misery.

One last important point........make sure that any replacement crankshaft seals have been purchased from a reputable dealer. There are some seals, available on the market place, which are not up to the purpose and quickly deterorate once bathed in hot engine oil. This also applies to the timing cover seal.