It appears to be seeping a bit. No, that is not normal. Is it urgent? probably not.
My question would be how long has it been seeping?, and is there still enough gear oil in the axle.
With the 4Runner parked on level ground, I would remove the fill plug, and check the oil level. With the truck parked level front-to-back and side-to-side, the correct oil level is filled to the bottom of the fill plug hole.
How can fix that? I don't have any drop etc. I just need to replace the gasket on the refill plug right?