5th gear headache

The snap ring pops out because of too much load on 5th gear. This comes from large tires that put the transmission under extra stress which pushes on the clip and pops it out.

If you are still running the same gear and tire setup as you were when it came apart, you probably ought to fix that first before trying another clip. Regear or ditch the large tires.

That said, there are kits on the market that can go onto the 5th gear shaft and clamp down to hold the gear in place. Basically they are an alternative method of holding the gear instead of the c-clip. One of those solutions might suit you better.