Are you sure you're on the bearing and not the pulley?   Under tight will cause slip and friction.  How fast you running the rotor?  Possibly not pulling the material through fast enough?   It's a Claas, speed it up is almost always the answer.

We've never used corn head grease, just the same grease we service the machine with.  We fill the entire cavity. 

Not sure on the temp but 200 seems a bit high but I bet it's pretty warm in there for just being this time of year.