I wonder how a refrigeration sealant would work in that application.
The stuff I am thinking of is called Nylog. If it works for refrigerants and oil at pressures up to 280 psi and on threaded fitting on the hot side of compressor heads, it probably would work on mating surfaces for oil lines.
Disclaimer, I haven't used it for this so take this for what it is or isn't worth...
There are two different types. One is a thickened synthetic for HFC refrigerants and the other is mineral oil based. Kind of feels like stringy snot or slug juice..
http://www.refrigtech.com/nylog.html