Teflon tape on flare fittings is the deal. Try it, you'll like it.

No thanks, I'll stick with anti-seize compound.

I experienced the same problem mating the MSA Earl's SST clutch hose to the slave cylinder. The original 34 year old hose is not a tapered pipe thread. It is sealed by using a copper gasket between the hose flange and the machined face of the slave cylinder. I achieved the original design intent of the system by decreasing length of the threads on the Earl's hose from .683 to .456. Simply cut it off with a hacksaw and carefully deburred. Purchased a new copper flat washer with 10 mm ID and put it together. Doesn't leak and clutch works fine.

LanceM may be right about the "inverted flare" fitting but aesthetically it looks funny with those threads exposed after seating.