You're welcome. Yes a little TLC works wonders.
A couple of quick and simple checks. Make sure the voltage little Out(?) terminal at adjacent to the trigger level knob varies sensibly when you adjust the knob, on both voltage ranges (and knob pulled and not). Also check that you actually have electrical connection between the BNC connector and the PCB (you should be able to read 1M resistance on the BNCs in DC mode without having to take the lid off). It wouldn't be the first time...
Don't rule out the possibility of switch contact issues (or no-FM trouble) with the input trigger related push buttons either. Worth checking before assuming that it's the JFET.
Lastly, don't forget that the counter has a check function which should at least exercise the trigger logic (though probably not the analogue front-ends).
P.S. Looking at the picture, the PM6622/24/25 manual should be helpful for most functions, even if the control layout isn't identical.