FYI Guys, like I said (I think) if i found a solution I would post it. I found a thread that defined the o-ring in mm and converted to fractional inch measure. I went on the hunt for VITON o-rings that might fit. The info on the web defined the ring as OD- 32mm, ID-27mm, 2.5mm thick. The product I found is a stretch fit but does not leak as long as you get the cap on correctly. A better fit may be available but this works nicely. (at least on mine) The source is McMaster-Carr, part number is 9464 k85. The only drawback to the fix was that from this company there is a product minimum. 50 pcs. @ 11.xx (i don't remember the change). So I gave at least 2 to each person I know that has the M4. (will not work on the metal gas can setup) Now I get free breakfast at our favored restaurant before going out to the field. Good Deal I'm not married and don't cook.