Oil Sending Unit Leak

[Sloan66]

Couple of months ago I had a significant oil leak on my 307 which the board was able to solve. It was the old sending unit, where it had cracked. I have the non guage type dash.

I replaced it and it stopped the leak for a while. now it is back. It appears to be leaking from the threads. I have tightened it (using the correct type socket) and the sending unit is actually touching the back of the manifold to point I cannot tighten it any further.

Are there longer type sending units? Not sure what to do, I'm I right in not using any sealant as that would effect the operation of the sending unit? Or should I apply teflon.

Thanks