Got it appart! it's the five speed gearbox so I went and blew 520 euro on go faster bits.
The barrel broke, had to resort to a metal pipe and the BFH bashing on the piston to seperate them. everything after the crank is mint.
It seems it died because of the left hand crank seal walking out, I'll 3d print a tool to make sure that's inserted fully and not doing that again.
So next week it'll be shiny bits and the hunt for a suitable chassis.
A side highlight of my week, got to test ride a suzuki goose 350, on paper really heavy, but it was really chuckable, even with tyres from the 90's I was going a bit too hard after 10 minutes :D
Looks like a satisfying project