When I removed my oil cooler I didn't notice how it was installed. I am assuming that it is symmetrical and can go in either way (flipped top to bottom, evidently not end to end).

 

I just did my oil cooler seals last weekend as well. I had the same question when I pulled the element out and started looking at it and then realized I didn't remember which side was up when it was still in the housing. I took some measurements (diameter and depth) of the inlet/outlet (where the seals are) and found they were the same on both sides, so I assumed to could back in either way. I flushed the cooling system multiple times this weekend a went for a few quick drives and no oil/water mixing.

 

The cooler is shimmed.

I think there is a wider machined boss on the side that takes the white plastic shim which would be the side facing the housing.

T

 

I also measured everything and it looks symmetrical to me, including the bosses. I went through the documentation on Clark's Garage, the Porsche shop manual and the Haynes manual and there is no mention of a correct and non correct way to install.

 

my only concern would be to make sure you change your oil filter not too long after installing the cooler.
in the event you get it "backwards" you will be in essence backflushing 30 years of oil-junk which will luckily blow out into the oil filter, but might clog up a filter quicker than normal.