If you mean ATP AT-205 "Reseal" it might give you some temporary relief depending on the condition of the seal. Be sure to adjust the dosage for the oil capacity of your differential if you try it.

If it's just dried out, but otherwise intact, it may work, but if it's ripped or torn, it won't do anything. Given that it's on the driveline, and it's quite exposed, rocks or debris could very well have have gotten to it. You have 178k km on it, after all. That's a load of time to have been kicked up by rocks and other debris. 

If it's dripping then I would get it replaced. It shouldn't break the bank. I would also being doing a very thorough inspection of the rest of the driveline. Worn out seals might be a red flag that you have worn out u-joints, imbalances, etc.