AKFish,
Thanks, got it. The strippers are all intact and secure.
The bobbing I mentioned even occurs when it's stationary... something is binding up inside the pickup head when it is running, and the torque on the drive sprocket lifts the pickup head until it overcomes that friction, then it breaks free and the head drops back down. I need to find the source of the friction but it seems like there are about 100 places to look.
When I looked at some similar balers for sale online I didn't see compressor rods on any of them, are they normally required?