Another solvent that works better than Acetone is Prep-Sol Wax and Silicone Remover. Auto body paint stores carry that. Once again, you flood the area to lift out the grease and then immediately wipe the stuff off with a clean, dry rag.
The basic idea behind these cleaners is simple, they are designed to lift the contaminant up off the surface long enough for you to wipe it away. The surface MUST stay wet and HOLD those contaminants up in the cleaner for you to wipe off with a clean/dry rag. That is mistake most make, they let it dry and the contaminant ends up laying right back on the surface.
Clean several times to remove heavy contamination. Also, You clean first
, then sand. Otherwise you will just sand the contaminants down into the weave of the fiberglass and get a weak bond with the epoxy.