'Had same problem with the Sump Drain Plug, FIRST time I touched it!
(AND I KNOW Who changed the oil the time before and used 150Ft Lbs to
torque down the drain plug...I'm a jus biding my time waiting to witness his DOWNFALL!)

Relief was provided when I soaked the drain plug area overnight (Twice) with
AeroKroil and then clamped what was left of the stub of the plug in the biggest
honking Vise Grips I could find...Tightened them down with another set of VG's...
'Slipped a 2.5 foot length of 1 1/2" Galvanized over the end of the ViseGrips and proceeded to LEVER...
It seemed like the Pan was gonna wrench off the bottom end of the block,BUT
FINALLY the plug backed out 1/3 turn and I was a free man again!

HOWEVER,The "Irwin's" should make short work of your difficulty.

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'84 300SD sold
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