Front differential front pinion seal leaking

Depends on why it started leaking.
Option 1 is the seal just went bad.
Option 2 is that inside something is breaking which put to much pressure on the seal so it started to leak.

 

Try spraying it with regular WD-40, this will cause it to swell a little and buy you a some time before replacement. This trick does work in most instances unless you have something worn so much it is getting ready to fly apart.

 

Monitor it. Once it starts puking and covering your diff deal with it.
If you check your fluid level that will give an indication of how much its loosing.

 

Check the input for slop indicating a more serious internal issue, bearing failure or the like. If movement is found I say tear into it before more damage is done. Like pushbroom says if it's just a seal, check the oil level and monitor.

Listen for the air puff or build of pressure to leak out when pulling the fill plug. If so the vent is clogged and pressure is pushing the oil out. Who knows cleaning the vent may stop the leak. Seen it before.