Dan_Musicant wrote in news: snipped-for-privacy@4ax.com:
If tubeless,I'd put in an inner tube,and if tubed,a NEW inner tube. If tubeless,you could have a dented rim or bad seal on the rim from rust. Dismount tire,sand off any rust or corrosion,paint inside of rim,then remount tire. Others have already mentioned bad valve stem or valve,or buying a new wheel at Home Depot or Harbor Freight(HF may have an odd shaft diameter) I know HF sells a replacement wheelbarrow wheel,I've seen them at the local store.