I’ve developed a slow drip-leakage at the L/F seal of the front differential of my 4-cyl, manual-trani Base 4Runner at 700 miles after lube service. I suspect an over-fill. A second shop said the gear fluid might be “seeking it’s own level”, & once reached, “MAY” stop there, -but ALSO said the worst that could happen is the FRONT w/d would not be ‘usable’. I’m 1,000 miles now from trusted repair shop. Is this a “BIG deal” ? The seal in question IS several inches aBOVE th fill-plug …
First thing to do is see of the diff is actually over filled. If it is than let the excess run out. If it isn’t than yes the seal is a big deal, get it fixed.
It’s difficult to over fill. It is not critical that the oil is up to the level of spilling out of the fill hole. When the front end is not engaged I don’t believe anything turns and if that is correct on your truck there is nothing to worry about for now. Check to make sure the automatic locking hubs are not engaging and verify that nothing is turning on the differential when you drive. If nothing is turning there is no problem.