If It's cracked or chipped then My guess is It probably isn't delrin, but as mentioned replacing a butt cap is a pretty basic repair. I would always first recommend to someone to have the original maker do the work, but on a scale to 10, I would put the job somewhere in the 5 range or maybe even lower. As far as stopping any cracks, for what It would take to try to do that, IMHO you might as well have It replaced. It doesn't take that much more labor to do It right. Finish work Is probably the most time consuming.