A tight mechanical seal on any of these plugs is what was intended originally from the MoCo as evident of how the plug was constructed.
However, when one of them leaks, it's not always cost efficient or convenient to have the threads repaired especially if your on the road with a badly leaking or blown out plug.

• Below is a collection of ideas for sealing up the plug until a solid mechanical seal can done.

• Try a thread wrap just under the head of the plug and re-install it. To tighten, just snug it up, plus a little.
  • Wrap some sewing string just below the head of the plug. ¹⁾
  • Wrap some Teflon tape below the head. It's intended use is for tapered pipe threads, ²⁾ and the OEM plugs use straight threads.
    Use only enough to get a seal. Using too much could crack the case from the extra pre-load plus normal torque.
• Try a thread sealant.