Valve cover cleaning?

What is the safest way to clean the plastic valve covers off the car?

I am scared mineral spirits and other chemicals will dry out the plastic and make it look strange.

I've used brake cleaner and other solvents. If they happen to melt..head to the junkyard..at most they are $10-15

Solvents like kerosene and WD40 (which I think is kerosene-based) are very gentle on just about everything (even paint). You have to wait longer for them to work, though. Wet a cloth with them and let sit on the dirty surface for an hour or two, or even overnight, if you have the patience.

I'm getting to like Gunk "Engine Bright" degreaser a lot. It'* a water wash off and very gentle on just about everything. Again, some patience is required. (nothing cleans faster than carb and brake cleaner, and I use them a lot, but they can be really tough on certain non-metallics. If you know your plastic is linear polyethylene or polypropylene, then these kind of cleaners are fine).

Nothing will make them look strange besides a bad paint job. I'd clean them with almost any kind of cleaner or degreaser. I use brake clean as well, with a toothbrush. Though no real amount of cleaning in my experience has kept them looking great since they are usually permanently stained. They will get dirty easily. That'* why I cleaned mine well, sanded them with 600 grit paper, and painted them. That'* the best way to keep them looking great.

Castrol SuperClean. Nothing works better. Use a clearcoat designed for engine parts if you want nothing to stick, and make them easier to clean later.

Moving to Detailing and Appearance.