Bought mine used with 137K, and it had not been done. I took it to a mechanic, and he said that typically a shop will put a sticker under the hood if it has been done. I got to watch mine be replaced ... no good way to inspect it without tearing off just about everything you need to replace it. You may consider going ahead and doing your intake and valve cover gaskets as well, and going through the coolant connections from the front of the engine to the back. Mine was gunked up, so we just replaced the connection at the thermostat, the pipe leading to the back, and the connection at the back of the engine. If you dig that far down, I'd recommend replacing the various coolant hoses too, a couple of short ones on the backside of the engine that are hard to get to, but would be easier while you've got the upper intake off.

AND, make note of where the various bolts go for the covers on the front of the engine, because they are not all the same length, but it's not obvious that they aren't.