RF Mixer Probem

I am working on an old Heathkit Marauder transmitter. It uses a 9 MHz IF that is mixed with heterodyne oscillator frequencies for each of the bands. The het osc crystal vary from around 5 MHz for 40 meters to 25 MHz on 10 meters which is divided into three band segments, each with their own het osc crystal.  The 15 meter band uses a 17 MHz het osc and it works fine but the three 10 Meter segments with 25 MHz do not mix with the IF and what comes out of the mixer is only the het osc frequency. The IF and Het Osc are combined on the grid of a 6AW8 tube.

Each band has unique tuned plate circuits to peak the mixer  and on the three 10 meter segments there are 3 identical coils. These 10 meter mixer coils  all peak in the middle of the cores. 

I have:

Verified wiring and tested all parts in the mixer. (remember it works perfectly up to 15 meters.
Verified wiring on coils and measured their inductance and they are fine.
The Heterodyne osc output on 10 is the same as the working bands and I can see the osc and IF mix on the grid but the output is only the osc signal.
Tried several tubes

I have run out of ideas. What would make this not work with 25 MHz het osc and work well otherwise? I dont have spectrum analyzer but can see somewhat on  my scope. Also the IF has a drive level control that reduces the output from zero to full drive but on 10M the drive level from the IF has no effect.

Any mixer experts out there?

Gary K4MT