NO, please don't sand it! Any Marine store, RV store, most Ace hardwares, etc, sell Macguairs(SP?) boat cleaners and waxes. Macguairs offers various formulations, from something almost as abrasive as auto paint polishing compound, all the way to pure wax. I use the Oxidation Remover or Color Restorer on boats, RVs, and bows when I really want to cut away a layer of grime. Then I go to the polish, and then pure wax. Note: some stores will try to talk you into gelcoat cleaner, sold in most groceries for cleaning kitchen appliances, or whatever. It does not work very well at all. The finish on your bow responds very well to the same products that do well on boats and RVs. This stuff is about $12 a bottle, and you will want both cleaner and wax.
You can also try auto paint cleaners and waxes, and I think they probably will work fine, but I feel the boat and RV products work better. It seems like the polishes and waxes that work best contain carnauba(whatever that is!)
The black gunk may require rubbing with denatured alcohol or goo-gone type stuff....it may be nothing more than tape residue from tape holding on the camo sleeves.
A little elbow grease and these products will clean up any bow finish.