compression release???

[oneb1jap]

have a bashan sunl cg6 water cooled 250cc quad: been a while since worked on it so symptoms is : try to spin it over - it won't. might get one compression stroke - but not two. went with new starter, battery, wiring, valve adjustment, socket on flywheel - it will revolve
got to my wits' end long ago
haven't pulled the head because can't see a gasket on VMC,
under rocker cover is a hole off to side near intake.
I'm thinking stuck compression release.
Hope any of you can be helpful,
what to do
where to get parts, etc,
thanks