You didn't say how old the tires are, but the air leak you describe often happens with old valve stems. That's why most tire shops include new valve stems when they install new tires.
I've never used metal valve stems on any of the high-pressure tires on my trailers and everything has been OK. Don't know anyone else that has used them, either.
Have a great day!
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Virginia Deacon
2006 TrailManor 2720SL
2000 Ford Explorer 4x4 w/SOHC V6 with WDH
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