Assuming the E34 seals we are discussing are the ones fitted to the body and they are just shrunken but otherwise fine, my repair:
Buy one piece of seal/trim from a wrecker (any colour).
Remove threshold trim and cut the seal apart at the seam.
Re-fit the seal tightly onto its mounting flange while pressing back against itself to compress the seal/trim lengthwise.
By the time you get completely around the door you will end up with a 2-4 inch gap.
Cut a piece of the spare trim and splice into the area under the threshold. Use 3M black weather strip adhesive to make the splice air tight.
Problem solved.
Anthony
03/64 production
'91M5 - 11/90, was mine, it's Jim's now.