I don't know for sure. I'm only guessing, here.
I don't know why there would be any oil or grease inside a lens. Not enough to leak out, anyway.
If there is any lubricant inside a lens, it should be a very light coating. Too much grease or oil on small, precision parts causes more trouble than it's worth.
Could somebody have worked on it before you got the lens? That person might have put lube inside it.
The only other thing I can think of that might leak out of a lens is balsam cement.
Some lenses have their elements cemented together. Balsam is basically tree sap. It's distilled and purified but its source is the balsam tree.
The thing is, once the cement sets, it should become solid. I can't imagine why it would run out unless it was subjected to heat.
Most modern lenses don't use balsam, anymore. They are usually air gapped at precise tolerance.
Balsam can turn yellow or become cloudy over time.
That, having been said, I have seen movie projector lenses that have cemented elements which were overheated because some dummy projected white light through an open gate. In those cases, the cement does melt and get bubbles in it. I suppose, in extreme cases, it could run out.
Again, this is all just supposition.
I don't know any reason a lens should have enough oil or grease inside that it would leak out.
I don't know whether your lens has cemented elements.
Further, I can't imagine why oil, grease or cement would run out of a lens unless it was improperly repaired or subjected to abuse, especially extreme heat such as being left in an extremely hot car for a long time.
In any case, if the lens has been abused in the past (before you owned it?) there should be other symptoms. If it's a lens that you value and want to use, I'd have it looked at.