A can of Flat Fix.  Probably don’t need much in each tire.

You know that most racing tires leak air right through the rubber right? If they hold air for an hour that’s my minimum standard for sprint racing. Have you tried wire brushing or using 150 grit sandpaper. If you have some way to spin the wheel it makes it easy. You could also try a very thin layer of epoxy or JB weld.

Gif

The beads can get torn up mounting and dismounting tires. If I have one with a bead that is leaking I will debead the tire and rub a little rtv sealant around the bead. It has always worked for me.

This will sound very strange but I saw it work.   Down dish soap on the bead, don’t think I am crazy (as I did the guy who told me) until you try it.