You just need to replace the clutch. It's a wear item. The " teeth" start to go bad on the one way bearing. Eventually it will just freewheel.
Fitnessrepairparts. Com or Treadmill doctor. Com for Parts.
Well that stinks. Sometimes it's pressed onto the hub and you need to get the assembly. There is nothing to lube it's a sealed bearing from the factory. Once they wear out they need to be replaced
There should just be a small amount of grease inside the bearings . Any grease should work . Grease wont really help anything long term if at all. Once a part starts to go bad it will need to be replaced.