Replacement Seals/O-rings for Portable Propane Cylinders?

Thanks, Agesilaus. Like you say, I don't want to cobble this up since the risk is high. But yes, I am a big fan of the true "hardware stores" where you can buy just about any kind of oddball part you might need. Any RVer should be familiar with their closest hardware store (NOT the same as Lowes or Home Depot).