Massey 1328 Disc Mower Troubleshooting

I have a MF 1328 3-pt disc mower, about 6 years old, low use (about 300 acres).  At the end of last season it had a vibration/bumping when I raised it up to turn, then all of the time as I finished the last field. 

 

I did not have a heat gun but two of the rotors were very hot to the touch, the other four were not so hot.  Just ran it about 20-30 min and used a heat gun, all six gear boxes were around 90 deg F, and no vibration.

 

I checked the dip sticks in each gearbox and all were full to the top, one had blue color to the grease the others were brown.  Wondering if it might be the spindal bearings in a couple of them, and how to replace them. 

 

Anyone have experience with something like this?

 

Thanks!  I need to settle it before we begin cutting.

Massey 1328 Disc Mower Troubleshooting