We live full time in a 1987 32′ Rockwood in New England, starting in November 2011 so Propane is near and dear to our hearts. As we revived and grudgingly updated the quarter century old systems we danced around the 100 pound propane tank and its original fill valve. The only other place that I had seen these is on the VW type II Westfalia campers. Finally we couldn’t fill the tank again. Couldn’t find anyone willing to touch the tank. So we took the least intrusive route and disassembled the Auto Stop Valve and replaced the o-rings. We bought Viton o-rings because that what stands up best to halogenated cutting oils and the like. Never considered that propane boils at -40F. Buna-N is the material of choice because it works well with propane and stays resilient down to -40F. But we managed to keep most of a tank of propane and that was enough to allow me to order a modern 1-1/4 inch ACME thread double check fill valve and a 10% outage or bleed valve for the 80% fill line.
The solution is a lot easier than dealing with this early attempt at a solution without a problem. In the long run the only use that I can imagine for this Autostop valve is to allow operator-free propane tank filling.
The solution to the AutoStop problem is to replace this valve with two new valves, an industry standard double check fill valve and a 10% outage or bleed valve at the 80% fill line on your tank.
In some jurisdictions state regulations require that this work be done by a certified propane technician. Having these parts on hand may make it easier for your certified technician because for his day to day work these are not a high replacement item and would not be a stock item.
Here are the AutoStop patent drawings and description: