I see this often at work with stuff that hasn’t been breaded in a long time,
The grease goes hard and blocks the port solid, it depends how bad it is as to how far you have to go, an easy starting point is to grab a 1/4” drill.
Take the grease fitting out and with your hands wind the drill in and pull the crap out. Often this opens it up enough so it will take grease again. I’ve also had it where it’s still blocked so I made up a fitting that would go into the item with a JIC on the other end so I can fit a porta power pump to it and pump hydraulic oil through it to clear the blockage.
After that you’ve just got to strip it down and clean everything out
