Disappearing oil

That’s right. There was a truck that I had that would burn 3 qts of 10w40 in 100 miles, and I could not see it behind me, or could others following me. But they sure could smell it. I was down to running Valvoline 50wt racing oil WITH STP, and that dropped the usage to 1 qt per 100 miles. But that wasn’t fixing anything, just a stop gap measure.
I just got out of an '03 Merc with a bad rear main and it was using about the same amount, a LOT!
Got an opportunity to replace the vehicle and walk away from it, so I did.
It's another Merc, but a few years newer and so far so good.
Have not noticed any oil consumption issues with my '91, but I have been on a "Bug Hunt" with that one for a while.
But this is all Good info for future reference.