Sorry Michel. I had forgotten it was a Comet. However, the leak from the main bearing can be the same. In fact there is nowhere else for the oil to come from. None in the gearbox etc. and a dirty great hole behind the clutch to let things out. (Your other message has just come in.) However, blocking off the chain oiler cannot cause this problem but do make sure that the breather from the engine is not blocked. Excess crank case pressure can cause oil to leak past the main bearings but the chain oiler cannot be considered a normal way to reduce crank case pressure. If all else fails fit a 'D' breather temporarily to one of the tappet covers and go for a run. You might get oil out of that breather but you cannot get crank case pressure.