WLToys 12428 rear suspension trailing arm and upper link. I printed these to test PETG strength compared to the stock plastic parts. The PETG is not as flexible but seems pretty strong.
It's a pain to get the ball ends to work in printed parts so I played around with just a plastic part and so far, so good.
As always, use at your own risk.
Wrench to drive or drive to wrench?
If you're looking at buying a WLToys 12428 in 2019, mine came with metal gears which is a nice surprise (all except the spur gear). The diff was put together quite nicely but the ring and pinion were under lubed for my liking. The diffs are a little rough out of the box so some light duty break-in running is probably a good idea. In the diff, there are shims between all the gears and the surfaces behind them, so if you want to upgrade a plastic gear car you are likely going to need to find some shims to get it working smoothly.
MG Chemicals PETG
Print at 235 degrees and 70 degree bed for a nice strong part.