I also had a problem with a rebuilt Master Cylinder (bought from Kragens Auto Parts abd rebuilt by Cardone) and drove 1-1/2 years with a spongy pedal.
Finally the Pedal went nearly to the floor.
At the time I did not know were the paper work was to warrant the rebuilt MC. I decided to buy a new one which at that time Autozone sold for $60+ made by FENCO. That solved the problem.
Unfortunately when I looked up the AZ price for your 83 the new ones are now $86 each.
Later I found the paper work and exchanged the rebuilt one; and I guess I have a spare one. I hope the rebuild on it is OK so I can use it later.

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84 300D, 82 Volvo 244Gl Diesel