Hi Silya, I would be looking at a couple of things. 1) Can you tell us when you first noticed oil was down, was this through a routine check and if so how long has it been since you checked oil. 2) Oil just does not evaporate, I would suggest the seal has gone and needs replacing - could be something as simple as
fishing line wrapped around
saildrive caused seal to break down. 3) Is there
water in the oil that was left or is there oil in topped up oil now. 4) have you checked the other saildrive to compare oil levels. 5) when was you last
oil change.
Ozsailer