MB1933 thicknesser

Hi, had this mb1933 thicknesser for a few years now, not used that much and no problems until this week. The drive rollers stopped working in fast feed speed and normal in slow speed. I took the gearbox apart and cleaned it and put it back together. Slow speed works great but fast speed still works the cutters but not the rollers also I get the occasional trip out on the comsumer unit. Any ideas?