As several people said every time a NPT fitting is changed out each one will fit slightly differently. If something has been taken in an out a few times you will notice the timing of the hexes are different for the same fitting.
It’s an old wives tale that keeps being passed on in the marine
industry. Sealants do not cause a problem with conductivity. Prove it yourself easily. Put Teflon tape or thread sealant
on a fitting and screw it in. Then take your multimeter and check continuity between the base of the part and the block or whatever.
Every master mechanic
I have worked with uses something. I like Rector Seal yellow or Black. The are recommended by the professionals at the number one Cummins experts in marine
applications and they have a set of articles on this matter and maybe a video - they have so many.
How many times have you seen “sealed” tight fittings get a green ring on them over time. You may not see the leak but it IS weeping and the salt
buildup is the proof.
Use sealer. Like so many things we are told they are passed down from engineers that never work
on something they just design it and Theoretically they are correct. If all are stuff was made to NASA specifications. All we get is Chinese tolerances.
There is enough metal cut thru your sealer to allow continuity.