Update:
I tried the 303 on a canvas/leather case, and I like this stuff. I have a Jeff's c/l case that had some mud stains on the lid and when I finally got them cleaned off, the fabric was a bit blotchy. I cleaned the case exterior with Folex spot remover (from the hardware store) and let the case dry thoroughly. Set it in the sun and sprayed the bottom, ends and sides with the 303, let it dry overnight, then flipped it over and sprayed the top. Full, wet coats. When it dried, the color of the canvas looked a little richer (kind of like your truck after you wax it; same color but better), and the leather had a nice, soft sheen. No discernable film or residue on anything. The blotchiness from scrubbing off the mud is a lot less noticeable now. I masked off the locks and hardware, and the 303 did not seem to soften the tape adhesive (3M Blue Painter's Tape). Tape came off cleanly.
I like the 303, and highly recommend it for protecting new cases or refreshing old ones.
