I did remove that panel and there was some dusty grime there, but not like the OP's impaction.
However, I thought while in there, I would check the switch setting. I wiped the area clean and used electronic clener to clean the switch and its mounting plate and bolts. The switch function is effected by the adjustment of neutral centering adjustment and that centering adjustment can be afftected by the park brake adjustment. So I also cleaned all those areas and adjusted the park brake to spec. Then I placed the Ventrac with all tires up off of the floor and did the centering inspection and found the original setting was still correct.
So, onto that little neutral switch; it was a PIA to adjust and mine was tighter (0.3mm) than spec (0.8mm to 1.6mm). The adjustment specs are given in tenths of milimeters and the distance between the measurments sites is close to 8.5 centimeters -- so we are talking frog's hairs here. I finally lucked-out and managed to get the switch set to near center of spec (1.1mm). If if you do this, I had the best success by just barely snugging the front switch plate mounting bolt, leaving the rear one a tad bit loose while the measured gap for the switch was on the "too wide" side, then gently tapped the mounting plate forward with a drift punch and small drifting hammer. I did the two measurments with a digital caliper and, having no helper to move the SDLA lever, I used a wood block and door framing wedge to shim that lever forward until the switch opened and to hold it steady there. I do not think a helper could hold it steady enough anyway.