I have had an interesting problem with grease zerks on the shaft for my fertilizer spreader. When I first mounted it I did not pay attention to the shaft length thinking that it was not a big deal. Well I guess I raised the 3 PT too far and jambed the shaft onto the spreader and broke off both zerks, the grease fitting broke off leaving the body in the shaft. Armed with a sledge I turned the spreader upside down and beat on the shaft for oh, say an hour or so, and it finally came free.
So now I cut the shaft down by about 4", put the spreader on again, fired it up and start working. I must not have been paying attention becuase I did it again, I broke both zerks off and jambed the shaft back on the spreader. Idiot I thought to myself.
I learned this time that the zerks break when running the spreader too low and I took another 1" off the shaft to prevent the jambing condition.
I find that I can't make the shaft short enough to fully raise the 3 pt arms and still have it long enough to have the recommended 4" when it is near the ground, so now I am just careful and I keep a handful of 6, 8, and 10 mm zerks in the tool box because the broken ones now litter my yard.