Some
inner tubes that come from Asia have quality issues, not
so much with the tubes themselves but with the valve
stems. When they fail, it's usually time to replace the
tube... but not always.
I once bought a 1957 Ford Ranch Wagon, and
the back end of it was full of old truck inner tubes. I
saved a couple, and I'm sure glad I did.
I punched a 1/4" plug out of some of
that inner tube rubber...
...which will get stuffed into the valve
stem cap.
A tiny dab of grease completes the seal.
Since the valve stem leaks, this guy gets a little extra
twist with a pair of channel locks. Presto, no more
leakage.