I use Scrubbing Bubbles bathroom cleaner on plastic parts when disassembled, works great and they all look like new. I just spray it on, let it sit for a min, then quick brush with a toothbrush and a dunk in a water bucket. Works great on fresh rebuilt shocks to get all the shock fluid off the outside. Pretty sure back in the day I would spray it on all the arms and stuff at the track then just wipe off with a rag between rounds. Doesn't leave any residue either.

I can't stand using wd40, seems like no matter how much I blow it off afterwards there is still a dirt attracting residue.