Plastic filament won't work for bearings here, because the bearings must move
freely on rods even when twisting pressure is applied.

My main problem is a dire need to make 8 mm bearing seals that actually fit
the 8 mm rod. The silly rubber seals that come with cheap bearings have a gap
wide enough to allow tiny particles into the bearing.

Any ways to make close-fitting but easy sliding bearing shields out of
whatever material?

Thanks.