Circular clip in brake caliper piston problem

[Hvnfn]

OK, this may be obvious... but, I have a problem with that little circular clip that is holding the parts in the rear brake caliper piston. Mine doesnt want to stay in. Ive had this apart twice now because the e-brake doesnt want to work because of this part. Do I just stretch the circular clip and reinstall it and hope for the best, or what would you guys suggest? I dont want to get it all back together only for the stupid thing to come apart again! A rebuilt caliper is $90 and seems overkill... but, I will if it is the best choice... just seems like a waste.

Im talking about this part:

[dmwhiteoak]

If I remember correctly, the clip fits snug in a groove. Is the groove clean and undamaged? Someone on here is selling a set of 4 that has recently been rebuilt for 100.00. I would buy them before I spent 90 for one.

[Hvnfn]

I decided to buy a box of assorted internal snap rings and double up a set of those to hold the parts in... Bad idea? Why wouldn't they have used an internal snap ring to start with?