Oil like substance "yellowish" leaking from around my bathroom exaust vent, what is it!?

I have taken the cover off but was nt able to see anything except that the existing drywall for about 4'' to the left is now damaged!! I will go to RONA or Home Depot today but I am concerned as to what may of caused it? Any advice will help! ***little note bathroom is on the main floor of a bungelow and not sure if it is vented to the roof or the side of the house?****