If it was simply slip potted from one pot into a larger one, the outside soil could be moist and the inner original soil could be very dry. I Always break up the original root ball a little with my fingers (or other tools if necessary) when I up pot. This is also important so that the roots will move to the outside soil instead of just circling about in the root ball. Of course too much disturbance of the root ball can be just as detrimental, if not more so, than not disturbing the root ball at all.
I would set the pot in a large tub and soak the heck out of it. leaving it in the standing water overnight. Also, it might not be a bad idea to put the plant in the shade for about a week.
Good luck. It has done well for you the past 3 years and I hope it revives soon.