If the case is aluminum, you should never use teflon tape. That's most likely why it cracked in the first place. Take the tape off, tighten the plug, smear black RTV around it and cover the crack. Let it sit overnight and should have no more leaks.
It's not aluminum, it's magnesium alloy, as stated. And Teflon tape does not cause cracks, overtightening tapered threads in soft material does... And I didn't crack it! It was cracked when I got it (without tape) but
severely overtorqued. I really had to lean on it to get it unscrewed.
What size pipe thread. Some share the same thread dia. and pitch as common straight thread bolts. If so you might be able to run a straight tap thereby eliminating the taper that is spreading the case. I would then use blue loctite or similar thread sealant and call it good.
I thought about drilling and straight-tapping it, then using a matching plug with an o-ring head. It's been a while since I got under there but I believe it's 1/2" NPT which is 14 TPI. Unfortunately 1/2 UNC is 13 TPI...
