I gave it a weak TSP treatment and a third oxalic bleach. Then dry-sanded with a 320 grit and applied 8 thin coats of Minwax Clear Poly - lightly sanding with 320 in between each coat.
It looks a lot better than the original...
...but not quite as well as I had hoped. It is certainly a lighter tone and many of the stains didn't come out of the teak and much of the mold would not lift from the holly.
All in all, I'll take it. Thanks for everyone's help.