John Deere parts fiche page.....
https://partscatalog.deere.com/jdrc/?Origin=https:%2F%2Fjdparts.deere.com&locale=en_US&country-cd=US
To the mower deck.
https://partscatalog.deere.com/jdrc/sidebyside/equipment/57029/referrer/navigation/pgId/2695134
The tensioning bracket is GY21401 John deere put sealed bearings in many of the newer products so all greasing does is keep moisture away. The aluminum spindle housings wear, and the bearings will be loose in the housing after a few years of use. John Deere sells the whole assembly at a reasonable price, and Stens sells a quality replacement assembly at a better price.
Another trick for getting zerks with hardened grease in them to take grease is to heat the zerk a little with a propane torch to soften the old grease up a bit.
One other tip... The small black gauge wheels should be about 1/4"-1/2" in the air when mowing... the deck should be supported by the tractor lift arms, not the little wheels. They are just designed to keep the mower from scalping on uneven ground. If run on the ground they will shake the deck apart, and also cause the rear deck hangers to break off the deck at the welds.