Expansion Issues

[classical glass]

Hi, i have a 427 side oiler with the correct expansion tank from era. I recently had it chromed plated and that's when the problems started. I developed a lea at the slip joint under the tank I'm thinking of a type of internal sealer (something like a gas tank sealing application). I talked to the company who plated hoping I could have it striped and have it repaired but they said they didn't recommend it (it could damage the thin brass). Is there a product on the market that I could seal it internally? I'm thinking of a gas tank sealer. I found a product made by POR. Any one have any better ideas???

Thanks for your time.