Hi, I changed the oil and filter today on my daughter's  2009 Audi A4 Avant 2.0tdi  ( CAGC engine code )  and whilst  underneath noticed a bit of oil in the immediate area around what almost looks like an oil filter housing cap. 

 

The photo is taken from underneath looking upwards into the engine bay and the item is  in exactly the same area as the oil filter housing.

It seems strange having what is clearly a removable cap here but I'm at a loss as to what it likely to be.

Can anyone help and is there a serviceable item underneath this cap. I suspect that the very slight oil leak may in fact be coming from this black cap seal.

 

Thanks Darryl

I'm now pretty certain that the leak is coming from the oil cooler attached to the filter housing. Seems to be quite a common issue.

Glad you e got to the bottom of the leak. Youll need this looking at asap. 

 

 

Thanks , on this car the actual housing is all alloy so I'm thinking that a new oil cooler and housing gasket should ensure that it gets cured. The only part that I seem to be struggling to find is the very bottom O ring seal that fits inside the groove on the bottom plastic cap pictured. 👍