Just checked circuit again.
Looks like C13 filters the final stage voltage in this circuit.
Seems to be the only other possible candidate.

Edit.
Just realized my JP has the same 68 volt circuit as your board.
Tomorrow I will measure my voltages at various points along the circuit.
This may hopefully help narrow down the problem.

Thank would be great 

I did replace C12 & C13 already, so yeah I'm not sure.
As I said in my first post, the R15 resistor is getting super hot, enough to melt the solder.