Hi

I have the model that came with a plastic strip from the factory and it still graunched. Someone on here gave good advice about removing the little spring as tinbum says but also enlarging the pivot hole.

It worked for me on the whole, however from time to time the graunching still comes back. It stays for a few shots then goes again. I'd say it's got rid of it about 95pc of the time. I am coming completely baffled and have learnt to live with it. I don't know a single 99 owner who hasn't encountered the problem. Mine is certainly leaps and bounds better than standard but not quite perfect.

You can buy the cocking arms with plastic in online but you may still be slightly disappointed.

If I had the tools, I'd be tempted to make a delrin guide as you say.

Let me know if it works