I may try one more thing - hex head socket 3/8 ratchet and 1' breaker bar.
Try having a second set of hands hold a 6pt socket that fits nice and tight on the subject in question... then give it a good whack with a hammer. Continue that until results turn up, hitting it a bit harder each time.
I use a small steel handled hammer that I 'hook' onto the bar as I hit it, to prevent a glancing blow. Of course, a glancing blow may turn the wrench sideways, rounding off a few edges in the process. Be careful. Usually with this method it requires minimal force to get the bolt to break loose, so go easy on it. A light, precise blow will break it loose, a heavy but poorly aimed one will wreck the nut.
Getting on it with big arms and a massive bar dramatically increases the risk of rounding off the bolt. Sudden and high torque applied will break it loose as opposed to a gradual twisting of a wrench really hard that may well just deform the bolt. Especially if it's all aluminum. I don't know what the front diff housing and plug are made of.
Hence, why an impact gun is very effective at removing stuck bolts when you have the access space.
The bigger and stiffer the breaker bar is, the more effective the hammer method is because it transmits more force into the target and isn't absorbed in the handle. I have a massive 3/4" steel bar with a solid head from NAPA, that weighs quite a bit, for the job. If it goes on the nut, no nut has ever said no.
Hope that helps. The Auto-pro bar I got at NAPA was worth the money. The princess auto special is a waste of time. They either round off bolts because they bend like licorice or they snap off at the flex elbow.
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