The plastic ones are not much thicker than paper, shaped like a tube with a shoulder on one end.
I have had mine apart, too, and decided not to replace the shaft or
plastic bushings, esp as mine was a little loose, not tight. Owners
neglect the shaft zerk, which is not good.
There are many parts of the HST pedal/swash plate control that can
get gummed up or corroded to interfere with smooth operation. I have
spent hours refurbishing mine. If anything, it snaps back to neutral
a little too quickly for my taste, even though the shock absorber is working.
BTW, the brake pivot shaft that supports all 3 brake pedals uses these
thin plastic bushings, too. A real pain to assemble.....keep them greased!