You may have an older ASA/Technik Engineering kit where the oil return line goes back to the side or underside of the oil pan. To make this possible, 3 holes have to be drilled and 2 of them tapped with M6 thread. The idea is to use a Banjo fitting for the line to be attached there.

Typically, a banjo fitting set consists of the following:

You have two copper crash washers, a banjo bolt and the banjo fitting (usually with barbed end). But for our application there is a flange. Below is an old picture taken by Zolti.

The red arrow points to the flange which is held on by two M6 screws (green arrows).

Due to wear and tear, oil leak might start to appear around the perimeter of the flange and the M6 screws. The fix to this is easy and does not involve retapping or drilling.

1. Remove the oil return line.
2. Remove the banjo bolt.
3. Remove the M6 screws.
4. Buy two 1/4" x 0.25" or 0.375" long rough threaded screws (much like the one below). Remember not to exceed 0.5" in length, otherwise you might 'hit' the oil pump housing.
5. Replace them as the new 'M6 screws'.

M6 and 1/4" machine screws are very similar in size with the SAE size being slightly larger. This is perfect for our fix. This tip is provided none other than Zolti himself. We tried it on our own setup and it does fix the leak temporary.

HOWEVER...

this procedure is not a good fix. Reason is you need to use reapply the RTV Silicone seal (or gasket maker) between the flange on the oil pan. We recommend Permatex® Ultra Black Gasket Maker or similar. See the green arrow below. You will have to remove the flange and the two original M6 screws. Clean the oil pan side and the flange side. Apply the gasket maker to the flange side. Reattach, let cure for 24hours.

Addition, I would recommend M7 screws instead of the 1/4". The particular M7 screws that will work has a BMW PN: 11121718856 and it looks like the one pointed by the red arrow below:

This stud has a M7 and M6 side. We need the M7 side. This M7 stud is perfect too because it has a short thread height so that you won't hit the oil pump just on the other side of the oil pan.

Note that you will need a M7 hand tap to properly tap the flange and the oil pan. We had a 1/16NPT tap and that surprisingly is a M7 size.

This fix will be good for a while if your setup is a daily drive. If you are tracking your setup, we would recommend weling the flange to the oil pan for darn good. See red arrows below.