Doesn't sound like the B2 piston but hey, I haven't had that experience yet so maybe it is, if so that would be a blessing!
oh yes, Lots of sympathy, 85drtysthbenz
I lost a trans in my '79 (with '85 engine transplant) and it turned out the valve body cracked. I jumped on it and it stuck in 2nd gear. fortunately I was less than a mile from a shop. If that had happened in West Texas places like I was at last week, I'd really have been up the creek and no paddle.
It cost me $2500 for a rebuilt trans with some begging, a bad core you know!

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!