John,
the best thing i found for preventing flared fittings from siezing is a little anti-sieze compound (found at all automotive stores)on the threads upon installation. note clean threads and make sure they are dry before adding anti-sieze compound.
hope my suggestion helps!
p.s. do not put teflon tape on theads because the is a interferance with the threads and the double flare will not seal properly causing air in and fluid to leak out.

Teflon tape is NOT a good idea as there is a posability that tape nay break loose and clog uo the break system, this I was told some time ago by a teflon rep. who was doing a demonstration using teflon tape at the shop (hydraulics)

Please don't use anything but what the brake manf. says to use, I make sure ALL oil and grease is cleaned from all surfaces, use a good commercial brake cleaner and when the cylinders and lines won't hold pressure from corrision and wear replace them, most are availiable at a reasonable cost, from Auto supply companys, NAPA has all of the ones for my 57 truck, 51 Belair, and the 53 Belair. there is no disrespect in useing parts from someone that don't require an arm and a leg just because it is a "Classic"

Johnny, have you found a solution to repairing the Hydro-vac unit other than a $250 rebuilt unit? That seems to be the most expensive thing on my 57 C6500, I was lucky the farmer that owned the truck spent $700 on brakes a couple of months before he sold it to me for $200.I found that one of the bleeders on a front wheel was rounded off and the bleeders on the hydra-vac were covered with several years of dirt and grime, and had never been blead. I ended up useing vice grips to break the bleeder on the front. and after cleaning with a pressure washer the hydra-vac blead ok.
I also invested in a Mity-Vac unit from J.C. Whitney and suck out a volume of old fluid a couple of times per year from the old vehicles, It is quick and painless, keeps clean fluid in the systems and removes the moisture, I suck out a small bottle full from each wheel and refill the reservoir between doing each wheel.

You know I don't know how I managed to have time to work before I Retired.