This is usually caused by one of 3 things, 1 you over-tightened the glow plug,2 you cross-threaded the glow plug or 3 you changed glow plugs so much you wore out the threads and then stripped them by over-tightening the glow plug.
I believe on the K4.6 you can just replace the head button. Some engines the whole head has to be replaced.
Yea i think i my have over tightened it and the k 4.6 you need to replace the whole head the newer f4.6 has the button. I ordered one for 12 bucks cheap fix thank god.