I am hoping someone can shed some light on a leak that has developed on my 94 Cabriolet. I just noticed it the other day while checking on my car in storage. A small wet/oily spot under the rear of the car almost dead center under the trunk. It seems to be coming from a black round plastic access of some type. It is well past the rear suspension area so I'm not sure what it is for. Due to fact it is in storage I was unable to investigate further.
Hoping someone can tell me what I was looking at and possible cause.

Thanks

 

Different oils have different smells if you've learned which is which. If you or someone you know can smell the difference between brake fluid, hydraulic fluid, 90W (differential), that will help you figure out what system is leaking. If it's not a Quattro car, it's not 90W. Since you don't mention any brake issues (leaky lines will drain the fluid reservoir and trip the fluid level warning light), I doubt it's a rusty brake line. I'm going wager since it's a Cabriolet, it's probably a leak in the hydraulic system for raising and lowering the top.