How do you take care of your HPCs?

It seems the casing of most of the Handheld PCs is made of ABS plastic. Since most of them are very old (about or more than 20 years), they may suffer from aging and weathering at different degrees. These vintage machines can only become more and more rare, and so more and more difficult to replace, how would you condition them (or simply don't care)? What are the recommended ways to prolong the life of the plastic casing?

I am asking this because some of my old collections (e.g. Toshiba Libretto) have shown clear signs of deterioration. Some of them have developed thin lines or cracks and are prone to break particularly in the corners and around the screen hinges and edges.

This is what I have heard:
- Avoid using strong chemicals to clean the plastic
- Rubbing (Isopropyl) alcohol may actually damage the surface
- Sunlight may decolor or even deform the material
- Soap and water is milder but still effective

I am not familiar with the chemistry at all and I just want to know if there are any tried and true methods.

(not a recommendation) I have used 64% isopropyl on a number of my devices, especially if came to me in poor condition.

I have thought about trying a commercial product such as this:

http://www.autoglymprofessional.com/en/products/plastic--trim-conditioner.html

But so far, have not been game.

Anecdotally I've noticed that the more expense that went into the production of the original plastic, the less likelyhood of it developing cracking and fragmentation issues. Iomega ZIP drives are notorious for cracking, for example. But laptops from a similar era tend to hold up alright.