Kerosene is too thick to really pentrate, even over long periods. I've never used the vinegar method although I have done several old trators also, but usually with WD40 or some other penetrating oil, sometimes left in for weeks and for the really stuck ones 6 months.
Further really nasty methods are:

A big block of wood and a hammer on top of the piston. (disconnect the con rods so it's one at a time).

Warm up the block and use dry ice or liquid nitrogen on the piston as well as the wooden block and hammer. I have had one that I was defeated by all of the above.

These harsher methods however may not be a good idea on a 'modern' lightly built piston and block such as yours... It desperiate stuff if you do.