If that delrin piece had a cup hollowed out in it where the lower end of the kingpin and spring sit it could be filled with some sort of damper fluid to dampen the kingpin movement. We sometimes put heavy syrup on the kingpin itself, but this tends to attract dust and fuzz, and doesn't stay in place for long. If that delrin lower piece acted as a reservoir for the fluid it would both keep dirt out and keep the fluid from leaving... anyways, that's just me speculating.

Alf, VERY nice work there. Can I ask what sort of mill you are using? I am about to purchase a cnc machine myself to cut carbon parts and I'm having difficulty deciding on which machine to buy.