95 A6, oil leak (steady drip)

so i just changed my oil today in my A6 (2.8). when i pulled off the oil filter, the entire shaft that goes through the oil cooler into the oilpan came out with it. i talked to a tech at the audi dealer and he said i should be able to thread it back in, throw the filter on and be fine. well, i did that. now i'm losing ALOT of oil from that fitting (not where the filter meets the oil cooler, but where the cooler meets the oilpan.) is there a gasket or o-ring back there that i could've ****ed up?

Theres an o ring on the backside of the oil cooler. There is also supposed to be a 22 or 24mm nut on the shaft that holds the oil cooler on.