When I put my gauges in from dieselmanor.com, the advised against using grease in their instructions. You actually are better off doing it dry, becuase then you just press a shop vac on the hole and suck it all out what if anything that did go in the hole. If you greased it, its all going to stick inside and wont come out. When I put the probe bung in I did put a dab of antisieze on that. :thumb:just be carefull if you crack it you're really messed. get a little grease on a new bit and go slow. also use grease on the tap to keep the shavings out of the exhaust and go slow with it too. the key is slow and easy. and don't over tighten the probe either got it. slow, soft, and easy.