The header drive sheave should be slowed all the way down and you should disconnect the hydraulic hose. The oil would definately cause your header and feeder to slip. The seals are no trouble to replace, but you don't need it connected in beans.I had to stop machine and pull out green stems from behind the rasp bars. Took bean head off and cleaned out behind feeder beater. It's clear now but I don't think it can handle the stems. My beans are real tall with thick stems. I also had a big hydraulic leak coming from the hydraulic control hose where it inserts into the main clutch shaft on left hand side of combine if your sitting in it. A seal is bad. The main clutch shaft is in the center of the drive sheave that runs the traction belt. Would this effect the machines ability to chew up the stems? Not much of a mechanic guys. Any info would be great.