probably a single,the dbb stuff from tnetics is fairly new like 2 years.i have another 64mm from them right before they changed to the new cartriges and thats still a single
i cant see how you would have a dbb setup.the tnx dbb line your looking at 2200 easy for a smaller unit.what you can do is look at the model number on the tag on the compressor cover and call them,see what you have but either way their bb big shaft units can handle thicker syn oil with higher oil pressure from the various units i have seen.
Put the GN-1 drain back on for now as it is the only thing I have now. If the prices where not so stupid for a new one, I would get a new, factory reproduced one.
After looking for one now, I gave the one I had away.