Leaking metal Tyre valve stem?

Hi My sons car has alloy wheels, and metal valve stems, there is a tiny leak between the valve stam and the alloy on one wheel, we are struggling to get anyone to repair at a reasonable cost. Would tyre weld make a permanent repair?. Some tyre specialists won't touch the wheel, one other wants to drill out the stem put in another, which sounds a bit drastic. Any other ideas?, is it feasible to get the metal valve stem replaced by a rubber version?. Apparently the metal ones get curbed and then start to leak.