Be very careful using MEK. It attacks most plastics. It will instantly ruin most countertops, and many floor coverings. It will damage most painted surfaces.
As you can see from this list, Kydex is pretty resistant stuff. A few items do stand out on this list as hazards to Kydex that you might encounter in everyday life.
The household name for Acetone is nail polish remover. So, keep that away from your kydex products.
Toluene is sold at building supply/home stores. It's another strong solvent especially good for tape and label residues and as a degreaser.
Carbon Tetrachloride hasn't been sold to consumers for many years (it's been found to cause cancer and birth defects). But, it was a popular cleaning solvent (often sold as "Typewriter Cleaner") for many years and you might still have some of it around.
Trichloroethylene is another that has not been sold to consumers for many years (concerns about ozone depletion). But, I've still got a big bottle of it (don't tell anyone). It was commonly sold as an electronics cleaner and was also the key ingredient until a few years ago in the popular gun cleaner "Gun Scrubber". (The new formulation for Gun Scrubber, BTW, contains even more agressive solvents and you really need to be careful with it.)
As I recall, people have previously posted that DEET, the active ingredient in many insect repellents, attacks Kydex. This wouldn't surprise me as DEET attacks many plastics. (Really makes you want to spray this stuff all over your body, doesn't it?)
Xylene is not on this list. It's sold in building supply/home stores, even grocery stores under the name "Goof Off" (others too), and will attack many plastics. It's a great solvent for label and tape scum on blades, though.
Gasoline is not on this list. It does attack some plastics. One might suggest that it is save since oils and jet fuel don't attack Kydex. But, gas is a much different product and it often contains other additives. Maybe someone has some experience with gas on kydex.
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Chuck
Balisongs -- because it don't mean a thing if it ain't got that swing!
http://www.balisongcollector.com