I'm about finished refurbishing my second lantern, circa 1936-41 Prentiss-Wabers 742.43. Bought it on Ebay and am awatiing a gasket and leather pump cup to arrive. Hopefully it will light up and provide more "Hiss therapy" in the evenings...
I've got a leak here (see video) and need help. This round O-ring I put on it doesn't help..... Lantern
I'll have to check on my L43S, I know they are not the same model but I don't think mine has a gasket where the pump tube meets the fount. IIRC the pump tube just threads in until tight.
Just checked my L43PA - same model different number - and there's no gasket between pump and fount. As @Kgam1020 says "the pump tube just threads in until tight." If you can't stop it leaking, you could try a little Teflon tape on the threads.