Okay guys, there is a mysterious leak through a rubber plug on the left rear wheelwell behind the wheel. There is this plug that has a hole in it you can pull it out and it reveals some kind of drain which was oily. It's giving off 1-2 drops of oil (I suspect ABC hydraulic oil but not sure). Is it the rear valve block leaking, no other errors or problems with the car as it keeps level goes up and down and doesnt sag. Any suggestions will be greatly appreciated

 

Can you take a photo to show where it is leaking from? The Pentosin has a distinctive smell...you may be able to tell what it is from odor. Or color, if it has been changed recently.

 

Yes, it looks like this after removing the cover of this drain. Is it possible to be trunk drain because I accidentaly spilled a little motor oil some time ago