I'll bet that door has worn out hinge pins and is sagging quite a bit, causing that door latch to hammer the striker when the door is slammed shut. You can clean that hammered piece and weld some metal back in and weld the piece back on.
I'd rebuild the hinge first so that you don't bang into it anymore.
Once you have the hinges rebuilt, put the door back on and adjust it until the belt lines of the cab and the door match up
Do this before you replace the door latch and striker.
