8 row vacuum here too.    Mine is  down to  the outboard  wheels  doing the work.   Seems  ok.  But,  my soils are   sandier  type and  slick conditions are  rare.

Did  a  whole  rebuild on it   last year,   I   just torched out the  hex shafts and  started over fresh.     For   the amount of  rust and  scale  and  each bearing  hopelessly fused to the shaft...   the   90 bucks  for   replacement  shaft was a no brainer.

IIRC,  the only thing that locks  the shaft is   the  coupler pin  at the  transmission.     The hex bearings  are  slip through,  with no locking  provision.   The  drive lug  ratchet  will be    set screwed to the shaft,  and  possibly   hopelessly   fused to the shaft as well.. So  cutting  everything out in   bite sized  chunks  made it easier to   heat and press off  the  re usable stuff in the shop.

Got replacement hex shafting  from Shoup.

I had 2  modules  and  their  frame brackets    extremely  worn on the pivot part,  so  I took  some   3.5 and  3 inch round tubing,  .25 wall,   about  3 inches  wide.. with  ZERKS. Welded  the 3 inch to the frame bracket,  the  3.5 to the  wheel module.    I had to move  these  to the inside location  because the bearing  pocket  was totally gone.  That's  why I only  run  the 2 outboard  drive chains.   Cant  put a  chain on  an   unsupported   shaft.   Now there is   a   3 inch wide  bushing surface  as opposed to the   factory   1/2 inch.. plus mine are now greasable.