'71 Heat/defrost problems

[Murphy IRE]

It's a K20 with a 400sb. The heat is always on and very little makes it to the windows on defrost. I've ordered a new heat valve and will install tomorrow. The PO installed an OEM A/C, I don't know if it has ever worked. I'm trying to determine why the fan doesn't work on high (separate thread -I have located the heat resistor and A/C relay). I'll check them tomorrow.
But I found two more problems The "S" Duct is all torn up. The PO used silicone and tape (NOT very well) and there were huge gaps at the connection. I see I can order one from LMC for $13+. If I can't repair, that's an option. THE REALLY BIG problem is the Duct Air Selector box. The flap works fine, but all the rubber is gone leaving a 1/2" gap all around on the inside (LMC=120+). I think I can "Gerry Rig" some rubber and adhesive and put the $120 toward taking my wife out to dinner.
Has anyone had to made a simular "Rig"? If so, what matterial did you use to make the new seal?
Any other thoughts on the heat and other suggestions, A BIG THANKS in advance.