On my TRS setup I have the oil cooler adaptor, it has a outer O-ring and inside it uses a paper gasket to mate to the block, I cannot find that gasket, when I took the engines apart, one was sealed with silicone, no gasket, i would like to find the gasket.. the part number is 27-99893 I am pretty sure, it is paper, outer is rubber.

If you can get a decent pattern off the mating surfaces, just buy some gasket material and make your own.