Does it need to be fully swapped out? or is it repairable? Could it be that sensor?

 

The sensor is not a source of leaks. While some have patched it, I think you will find the plastic cooling system parts have become brittle with age and heating cycles. Considering the risk of severe damage due to overheating these engines it would be my choice to replace it.

 

Replace. Last thing you want is an 85 mph reservoir burst and overheat.

On a side note, I purchased a coolant pressure tester this week for my fleet (family of 6 drivers) and it has already paid for itself with the first use. (didn't have to hunt and peck for the leak it showed up as soon as I added pressure) If you do not have one, spend a few bucks on it- well worth the $.

 

Sensor was the source of the leak... Replaced the whole tank

 

Well, the well that the sensor clips into may have been leaking, but the sensor itself is external to the tank

 

Yep - BTW, Gus has a good write-up on the sensor on his website.