Give it Up
Ron, I have a 83 OD34 that had the original fabric in it when I bought the boat and the same thoughts, that you have when I first got it. After long sessions of scrubbing and cleaning with different miracle cleaners, it looked worse than when I started. No matter how hard I tried, the fabric was clean but blotchy looking. My wife and I went to a few fabric shops and picked out some brighter stain resistant industrial grade fabric and had everything recovered. I pulled everything out and had it recovered at a local shop. The entire job cost 500. + fabric. Not only did it brighten up the inside, it got rid of the old "boat smell". It was worth every penny of it.