Best Way Sealing Fuel Gauge Sender

[dave205 19]

Ive recently removed my fuel gauge sender to change it for a non-faulty one, but i didnt use any sealant when re-fitting the the threadedplastic ring that holds it down.

 

Subsequently it now leaks and as its plastic i dont know what to seal it with, what do people normally use?

[dave richards 26 1 Cars]

should have a rubber seal iirc

[dave205 19]

It looked like someone had put sort of black sticky sealant on the thread of it, there was no seal on there.