The goodyear bellows have a clamp of aluminum. If you have a wormgear clamp it is possible it was added over the top of the original clamp. The bellows are available from Prevost. If it is not the clamp that leaks it is likely a crack in the plastic base.

Ken, I'm surprised you have manual adjusters. Typically, coaches with OTR always had pneumatic belt tensioners, except for converter installed accessories like a second alternator. Early coaches had brass air cylinders (which I loved because you could really polish them up). Series sixty coaches have the small bellows that look similar to generator air bags.