I ended up going with the Markforged Onyx because I had printers at work with the material already loaded, and it held up just as well as the PPS and PEKK parts during testing.
The PEKK design with cut-outs all the way down to the base was too flexible, but the oem design was too brittle and cracked when installed... so I made some cut-outs around 2 of the clips, and it's perfect.
You slide on the indexing nub, and smack it with your palm and it clips on super tight without any layer separation or cracking.
Now that I'm satisfied enough with this design, I should have the car running by the end of April. I think I'm gonna run these for a couple weeks and then pull the valve covers to inspect/replace with new ones.
I think this design with the little cut-outs would work in the PEKK (Stratasys Antero) without breaking, but I haven't tested it yet. The Markforged Onyx is way less brittle than the Stratasys PPS and PEKK. I've reached out to several Print-On-Demand shops and this design seems to run ~$80/ea in PPS/PEKK, so $240 for a set of 4. Which for only half the Slon option isn't that much of an improvement. I haven't quoted out the Markforged Onyx, but the required printer is wayyy cheaper than the Stratasys ones for PPS/PEKK, so I would assume it should be less. Regardless, 3D printing paraphernalia has been following a price/capability trend similar to Moore's Law, so these should be chump change to have printed pretty soon.
Assuming these hold up, I might move on to work on a spring steel/sheet metal replacement... or just keep printing replacements and go longer and longer between checking them lol
I'll upload the designs this weekend to Thingiverse... and here if I can? idk. Does anyone know if Solidworks or Blender/etc can import a Parasolid file to keep all the relations in case anyone wants to modify it rather than an STL/mesh that is a b**** to change?