Pinion nut won't move.

[C30Seenemall]

Hey all...

Trying to replace the front pinion seal on my rear differential.
My p/u is 1975 C30 454 automatic. I'm using a 3/4 drive 1& 1/2 " socket, reducing impact adapter and 1/2" impact wrench. Nut ain't budgin'.
Been using WD40 on it, but I'll bet there's something more effective.
There's no rust but it's been on there for 44 years, so...
I have no heat to apply it, (not sure I want an open flame there anyway).
I tried my 1/2" breaker bar but have not applied major leverage to it yet.
Not sure I have enough room for that.

Maybe I should capitulate, and take it to my professional mechanic.
Thanks in advance for your input and assistance!
"Not-Muscle-Bound" Wayne