Front hub leaking grease, new seal?

[New2PSD]

I'm not familiar with 4WD so hopefully this is a no-brainer for those that are.

This is an early 99 250 w/ 268k miles on it.

I was at the tire store getting some new tires installed and the tech mentioned that there is grease leaking out of the front hub on the passenger side. It is a small amount of grease but he said if I didn't replace the hub seal and re-grease it then I could lose the whole front axle.

So I wanted to know; is his diagnosis correct?

And is this so urgent that I shouldn't drive it at all until I fix it?

I don't know how long it has been leaking.

Thanks!