I was greasing my "new" truck recently. There were a few zerks that wouldn't accept any grease, even with a cheater bar on my gun handle. I'm most concerned about my king pin zerks. The steering is still easy, the truck doesn't wander, and the KP's aren't sloppy. I think I could keep it that way if I could grease them.

Is it worth trying to replace the zerk or would the plug be farther in. Should I try to apply heat or are there rubber seals I might damage. Are there any other suggestions?