A buddy on Classcomp asked that I re-post something I posted there. I have never heard of this particular forum but was glad to know of it and glad to perhaps contribute.
Every time I mention it someone responds with horror, but WD40 has been a terrific tool for me, is indispensable. It was plastic that was mentioned in the Classicomp post, brittle plastic.
I can’t guarantee that a totally disintegrated plastic can be rejuvenated by any method, but I’ve had very good luck with dusty-surfaced plastics, ones easily scratched, ablative due to age. A coating of WD40 will be drunk-in by the plastic, pretty quickly at first, and subsequent applications more slowly, overnight. Repeating this until the plastic no longer drinks the WD will rejuvenate the Surface of a plastic, at least the sorts of plastics used in many computer cases, the Atari computers (all of them), the bezels of floppy disk drives, faceplates of IBM PC/XT and just about any computer with a plastic shell. If got to early, the results are remarkable.
Other uses I put it to are to wipe contacts, card-edges, and to clean contacts and switches. I use swabs to apply it to the guide rails of disk-drive headsleds, to restore all kinds of moving parts. To access points I cannot use a swab on I use a syringe filled with WD40 to make precise, very tiny applications. This is especially helpful with floppy drives, as their most common failure modes are mechanical or electronic failures of the cascade variety, caused by sticky mechanical. A good example of this, and common, is failed darlington drivers. They fail because the motors require more power to move than the designed maximums, putting strain on the drivers and frying them. you can replace the driver and blow it again pretty quickly, but if you lubricate the mechanism (once in 40 years is not too little!), it will take the load of of a working driver or allow a replacement to live, a fair chance at life anyway.
As for retrobite, which was mentioned in the email to me, I’ve used the souse method to brighten keys, but larger items are difficult to do. I’ve been using paint, which the plastic also really appreciates, it being oil-based after all.
Thanks for listening and I hope I’ve given someone a hand-up. I’ve been working on computers for 40 years now, have had at least one of pretty much everything from Acorn to Zorba, and would not steer you wrong.