Not sure how it is attached on your car but can the filler neck be unbolted to replace the gasket?  I have not used the JB Weld tank sealer but they do make one.  

@david-jordan-2 I've been hesitant to reply to this thread because I have no direct experience with that year/model. Having said that I've not seen an OEM tank with an O ring on the filler neck. Is this an OEM tank or an aftermarket tank? I replaced the tank on my 38 with one from Tanks.com and it has a separate filler neck to facilitate shipping cost. It doesn't have an O ring but instead relies on short section of hose to seal the connection. I'd hazard a guess that the lack of response indicates few of us have direct experience with your issue. If you have an aftermarket tank I would recommend contacting the manufacturer for advise.

@tiny Good Afternoon, Yes, it is an OEM tank and filler neck. The book specifically calls for an O-ring between the two pieces. The sleeve like what you are referring to did not come into play until the 1957 Chevy for sure but not sure what they used on the 56, it could be a sleeve also as they moved the location of the filler neck to behind the left rear taillight assembly door. I wish the 55 was like that but it is what it is. I will reach out to some other forums to see if I can get any kind of a response from them. Thank you for your input it is appreciated.

@david-jordan-2  I restored my 55 years ago and have a little experience with the fuel tank and filler neck.

Did you use a little grease on the o-ring when assembling it onto the tank? If it was assembled dry, the o-ring tends to become dislodged and the grease helps it stay in place. But I have a better solution than grease.

When the tank is way below half, take apart the filler from the tank. If your o-ring is OK, reuse it, if not, get a new one. Clean the o-ring, tank, and filler neck thoroughly where the o-ring sits.

Instead of grease, I would recommend using a sealant like Seal All when assembling the neck onto the tank. Seal All is impervious to gasoline and is widely available. I bought it at Ace hardware, but you can find it online at Amazon too: https://www.amazon.com/Seal-All-380112-Contact-Adhesive-Sealant/dp/B008VK0JS4/ref=sr_1_3?crid=1K37H8SB3PNT&dib=eyJ2IjoiMSJ9.dbv8BXFeBvd9JXeNY2jKQl3ZOj02YT_bycg7vTJaBkCg-NhQWBTgV-bfB1grLJteC4--2J5eYUu4KvNyU6c-Omn8_0XxOobJcG6zC6VOOCyE_7siTjlZld_eED6hWNRnoXd7a7TXtEgof82a5RKEVQFetfYYWcSBP_k6-86HliovUGF4ri7Q-E9xQYhtZxlmhZ5nayzwLbg_BUDFrRIE46O5bGvV9iVbfPcgNL2hvYc.nadCbfcJbBUkCbjPqQ2ZcRrXKtwqqO6WQ1w748iTZHM&dib_tag=se&keywords=seal+all+gas+and+oil+resistant+sealer&qid=1719928095&sprefix=Seal+All%2Caps%2C387&sr=8-3.

Read the curing instructions before filling up the tank.

Good luck!