the mysterious freezing MB diff plug

[JHZR2]

Hi,

I have noticed an odd phenomenon which I do not see on the othewr differentials I work on, on my other cars. What I notice is that when I change the diff fluid in the 300D, afterwards I tighten both plugs to 44 ft-lbs. However, when I try to get the fill plug out the next time, it takes considerable effort, sometimes me pressing on my breaker bar with my legs to get it loose. I put my torque wrench on it today when trying to loosen it, and it takes way over 100 ft-lbs to get it loose, compared to the 44 that I tightened it to. What gives? Does diff oil (M1 is what I use) serve like a sort of threadlocker when it dries out?

Also, How sensitive is the diff to fluid level? I drained and filled it over 20k ago, so since I was doing the diff on my truck with m1, I figured Id check the MB. As soon as I got the plug out, fluid started gushing out. In actuality, my rear was slightly raised, so the plugs were at the highest point, yet a lot came out before I decided to not add and quickly plug it back before it looses more.
The thing is, I filled it correctly last time.

I had driven the car on the interstate about 45 minutes before I checked it, and it was about a 30mi drive. The diff was warm to the touch, but I figured it couldnt be warmer than if I did the job on a summer day, so it was no big deal. I cant believe the diff fluid expanded that much though.
Since I suppose the level didnt fall below the fill plug, am I still OK with regards to level? Does it make too much of a difference, even if the actual resultant level is slightly below the fill plug?

Can damage be done by the diff being filled slightly high?

Thanks,

JMH