I'm finishing up a complete 4-wheel drum brake overhaul on a '70 Super Bee (manual brakes). I had the original MC resleeved and rebuilt it myself using a Raybestos kit. Seemed to go together very nicely. All pistons and seals were replaced, as well as the copper fitting which go inside the outlet ports. I'm fairly certain I seated them correctly. Since I don't have a vice and didn't want to scratch the MC I installed it on the car and connected the brand new brake lines I purchased for it (from Fine Lines). Instead of connecting them to the distribution block, I attached some rubber hose rerouted back to the MC pots. Effectively, to bench-bleed it.
I noticed right away I was getting an air leak at the outlet ports on the MC, even though I had tightened them what I would consider "sufficiently". So, I cranked them down some more. Still sucking air back in.
I've now tried Permatex Thread Sealant on both ports and cranked them down pretty hard. There does not appear to be any leaks around the outlet ports now, and I cannot hear the air hiss that I had before; however, I'm still getting some occasional, small bubbles back through the hose when pumping the brake pedal.

If a MC is properly bench-bled, should there be any bubbles whatsoever coming back from the hose which is in the fluid??

It bothers me that i had to crank the fittings down so tight, and use thread sealant in order to get them to seal. I'm thinking perhaps the threads on the ports were galled/pitted some because the car sat so long and the MC was quite crusty (before being refurbished). I'm worried the leak will return when everything is hooked up and there is real pressure on the system.

If it makes a difference, I'm using DOT-5 fluid.

Thanks.