I have a 99 OBW 2.5 DOHC and the oil sender is leaking like crazy underneath. I replaced the sending unit (New Subaru Part) and removed and tried to reseal the little adapter under the sender while I had it apart. (It was also leaking) The threads looked good, but I was concerned the ground circuit wouldn't make up if I used teflon or some type of RTV. What has worked here for you guys.

No matter WHAT you use you WILL have continuity. It doesn't take a lot of contact and when you screw the pipe thread into the hole, it will bind and make contact. Teflon is good - pipe dope will also work. If you really want to overkill it - get some copper impregnated RTV - a little dab'll do yah and make a "trail" from the sender to the block. Or you could always put a wrap of 24 gage copper annealed wire into the fittings about 2 threads in and tighten it down - the copper will also act as a seal and provide your continuity