I would expect better results with Randy's "hammer a box end" tip, than with your "pipe on a breaker bar", believing that impact vs brute torque is more apt to be effective.

I have little belief or faith in any of the snake oils du jure, after repeatedly soaking a rusted on muffler clamp nut over a period of months—with both P'Blaster and Kroil.

This nut had been run on a used u-clamp by hand, then tossed in a box of parts under the bench. Now it refuses to budge (in either direction) with the 1/2" torque wrench set at 50 ft lbs.

I know I can get this nut off with impact or more force. But the point is that these so-called "penetrants", applied on both sides of this nut, have had no observable effect on what must be simple thread rust and time.
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Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.