Good thing you are spot testing first....always a good thing when strong chemicals are suggested without the proper safety warnings or procedures.
Understand that even a small amount of that may dry out the vinyl, may not look bad at first but a few months down the road and it may just fail. If you can snip a little piece from under the seat and dip it in the MEK you'll see.
Funny I sometimes have to teach staff proper uses of strong chemicals. Good thing as most can't, or won't, read a label or MSDS. One of them used Muriatic Acid instead of floor cleaner on our tile deck once, good thing I walked in after smelling the fumes and could kick him out for some fresh air.
Etched the shit out of the stainless, that created way too many hours of repolishing, did not make me happy and also caused a lot of the tile grout to fail not long after. A very expensive mistake for the taxpayers.