Most of the older wheels had the centers riveted, not welded in. It's possible to get a slow leak at a rivet hole unless it's installed very tightly. Sometimes a good sandblasting job and several coats of an epoxy based paint like Imron will seal up leaky rivet holes.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!