My first question is how big is it and does it move or appear to heave when you drive across it, if it does, you have too much loose material in the subgrade and your gonna have an issue, if its holding water for a short time and has good sunlight where it can evaporate and seems solid when driving across it I'd leave it alone, if its holding for days or longer it will eventually do exactly as you suspect, I'm assuming its a 3 inch pad, if its thicker its less likely, if you dont want a patch and dont mind sweeping that water off you may want that option, it will always look like a patch. I think getting a reason why its low is the bigger question, and then just decide the less aggravating solution.
