I threw together a design with incorporated, printable bushings. I have not tried this out yet, nor even printed it, but I’ll share it in case some brave soul wants to try it out.
I think these would need some light lubrication, maybe a bit of mineral oil.
UPDATE: This part is a WIP and has a couple known flaws:
1.) The clearance on the bushings is too small, so they will need to be enlarged with a drill.
2.) The slots for the captive nuts is the wrong internal shape, giving them too much wiggle room.
3.) The front lower corners of the carriage are a bit thin, and so the structure is not as rigid as it could be.