Pin won't take grease

We've got a 304H Deere loader that has grease zerk that won't take grease. All 3 would take grease when we got the machine, but they were all difficult right from the get go compared to the rest of machine. All have steadily gotten worse to the point that 2 of them wouldn't take any grease. Both bucket tip pins and 1 lift cylinder pin.

I tried one of those grease joint rejuvenating tools that you fill with oil and tap with a hammer. Didn't seen to do anything for the 2 that stopped...

Pin won't take grease

Pin won't take grease