The plastic long box used on sega cd, saturn and early psx games is a horrible design. Disc can come loose and rattle around Manual has a poor retention system. The main problem is that the manual will sag and deform, or even worse fall out and get crimped. However I have a simple and cheap fix. Get some acid free virgin(new) cardboard and cut to size, insert and instant manual protector.
I've been buying up garbage SegaCD and Saturn games when I find them solely for their cases. Usually scuffed up but shit anything is better than a cracked case with busted hinges. This is a great idea though, cheap and effective.
Welcome to Sega Saturn Cases in europe. Even from new they refused to hold the CD. The EA cases however were brilliant.