You say 2 - 3ml..... I wouldn't worry too much, it's an old machine , oil leaks of small quantities go with the territory. Keep an eye on levels, the engine oil, dip stick on the side of the engine. Transmission oil dip stick on the side of the gearbox under your seat. So long as they don't drop rapidly its likely all is fine. It's a job for the perfectionist stopping absolutely every leak.
Can you tell us where the leak is ? Most common on 135 is for the engine crank shaft oil seal to weep, this lets oil into the clutch housing, which has a hole in the bottom, specifically to allow oil to escape without causing problems to the clutch. You will see oil on the floor just forward of the gear stick if this is the case.
Cheers. Stu