I have a very slight leak in the fuel line at the center carb. The fitting is as tight as it's going to get. Is there an appropriate sealer I can use here? Or do I have a bigger problem? The carb bodies were completely remachined and replated, so everything is basically new. All the lines and fittings are new as well.
Oh yeah, the leak stops when the engine warms up.

I had a similar problem. The fuel line leaked where it entered the fuel filter. I disconnected the line and relined the threaded piece with new teflon tape. All better now.

Thanks! I wasn't sure if the teflon tape would be compatible with fuel.

Those fittings and lines should be a inverted flare. Make sure there is nothing like a metal bur on the seat on the fuel line and the inlet seat on the carb fitting. It could also be out of round. I would also make sure the fitting is not bottoming out so the line is coming into full contact with its mating seat.

Its most likely not leaking at the threads, but more like at the seat and leaking around where the tube passes through the fittings. If you have the right tool you can place the flare end back into the jig just to make sure its a good flare and has been distorted and retry the fit.

The leak is probably goes way after the engine heats up and expands causing the line to tweak a little making it fit tighter against the seat.

Thanks! I have a double flare set and usually make my own lines, but these boogers are so short, I thought I'd be better off buying the set.
I'll take it aprt and recheck the flares.