This is about the upteen diff. person this month that has had this happen to them. Here we go....
Yes, the Teflon tap can keep from making a ground. Usually, a teflon tape, when tightened, fills in the imperfections between the 2 threads, thus, sealing the leak. When you want to ground your senders thru your intake or block, while sealing, is to put just a touch of 'liquid teflon' on your threads, the first 3 or 4 threads, (don't lather the whole base of the sending unit down with sealant!) then screw it into a hole that has been chased. Check continuity between the base of the sender and the intake or block after installation, you might have to turn it in just a little to tighten the sender to get it to read....usually theres no problems. Just have to check...
Also, for the die hard purist electician among us, get a grounding washer, ie, a washer with a 1/4 spade connector onto its edge, (they do make them). Get one that fits the bottom of your sender, that the threads go thru just a little.
Then after sealing your sending unit, slide the 'grounding washer' on over the sender and screw into block.
While tightening, hold the tong on the 'ground washer', until the threads grab the ID of the washer, the threads will start to cut into the washer and the washer shall start to turn, get your sender where you want it....then you have a good mechanical ground....
