Front brake weak...

i understand your issude i has a similar one restoring my bike.
as for your resivoir, that gasket your missing will move to accomidate presure/fluid inside the resivoir. as for the bleeder nipple located above the banjo bolt that connects to the caliper, get some thread sealer on it after the system is bleed of air. also rubber lines are fine but braided steel lines are best. just remeber those coons can chew threw both

i relaced my entire system mostly with parts off ebay.ordered a new resivoir and switch for 15 bucks used some rubber hose from my old kawasaki, and completly over hauled the caliper.

 

I was able to do it, I think you can do it. Use a camera to chronicle your brake down, every time someone takes apart the master cylinder, there is that one thing, you can't remember if it goes big side in first or opposite. I will save you time from trying to dig it up, and then the attempt at looking at the photos trying to make heads from tails of the difference of the narrow end, verses the perspective larger end.

I went with metal tubing, I just had to use vinyl tape to fill the void in the cable holders. (I love the vinyl tape takes abuse up to 500 degrees Fahrenheit, etc...) it can handle filling the gap. The plastic/rubberized cover over my cable was not UV protected, so it has hazed in the first year of being on the bike.

2. No, Hydraulic stuff was designed to work without pipe tape. Something I like to do is with a clear hose that fits snugly over that nipple, Run the hose 3 to 6 inch's upward, then have a can or bottle to catch excess fluid, Use the Tube for working the bubbles out. Every squeeze will move bubbles out, Tighten it down, squeeze, open it up, top off the reservoir, and a attempt to do it again. Once your sure there is no more air bubbles, its time to close off the valves, and top off again, and declare its a done job, check list to see what else is on your plate to complete today

Oh hay, attention to detail, the Rubber top liner, should be some sort of harden plastic, (at least for the 81) and under that is a metal holder to help hold the rubber diaphragm in place. I have found using a small piece of paper, while sealing it, to be helpful to ensure the rubber stays in place till I can tighten that side down. But that might not apply to your 82 bike. Good luck Tobie