no idea...I made my own 'in line' shut off valve as nobody knew what I was talking about, at Oreillys, pep Boys NAPA etc...got parts from Home depot...cu the heater rubber line up high before the carb ,so its easy to get to...I turn it twice a year...winter use, summer use....no idea about caps...just think caps would be lots more permanent.
Mine didnt leak fluid to cabin ,just wouldnt shut off hot air flow all the way...and in Texas summer heat 90-105F ,its no fun with hot air on your feet.