If you figure this one out,, patten your method and you will be a millionaire.
Well,,Ok,,maybe not a millionaire but at least I would know how fix them.lol
Only thing I know that will work is a tube or sometimes if not too bad,,,,green slime will cure it,,or fix a flat.
Seems like just maybe black gasket maker might work but you would have to let it dry before putting air pressure to it. It won't hold much PSI,,so if it is real bad it won't work. But I have seen leaks like this where the air is barely coming out,,there's not PSI there.
I have never tried it ,,just a thought.
Make sure no one is around when you do it!!!!
But if it works????? hmmm???