I have oil leaking from a spark plug socket on my 1981 Volkswagen Rabbit pickup truck. Before you ask, it's swapped with the 1.6 gas motor instead of the 1.6 diesel.
The oil leak appears to only be coming from cylinder 1.
Here's a picture if that helps. Note that the engine is pretty filthy because it used to have a notorious valve cover gasket leak but that has been repaired. I just can't be bothered to clean it as I've tried a power washer and the stuff just wouldn't come off.
I do not know the mileage on the engine nor how many miles have been put on it. The odometer is broken and the previous owner said he does not know how many miles were on the engine when it was put in.
It did idle pretty rough but I ran some seafoam through and that fixed it. It also has brand new E3 spark plugs.
If you're wondering 'where's the question' my question is what is likely causing this issue?