New Gas Tank Sending Unit Leaks

Finally had a chance to get the sending unit out and fix the seal. After really comparing the new retaining ring against the old one, I am shocked to see the difference in quality. The new ring appears to be a cheapo stamped out piece of crap metal. The original one, nice thick sturdy ring. Why I didn't catch this in the first place, I don't know. Anyways, after taking in all the advice from above. I decided to re-do this only once. I cut another matching gasket from thinner material and put the two gaskets back to back and added a tiny bit of gasket sealant (fuel tolerant) to keep them together. I put the rubber one against the tank and the thinner one against the sending unit. I tightened the assembly down using the old locking ring. What a difference, nice solid seal. I won't find out if it leaks until this weekend when I get it out to fill up the tank again but, I am confident it won't.