[jimcol]

Not knowing how much you use the rig I would be more inclined to go with Rohrmann on the vent issue. Those mud daubers just love the heat of the pipe and probably the smell. Take a garden hose to the roof, drop it down the vent pipe as far as it will go and turn on the water. As the blockage gets more wet just lift the hose up a couple of feet and drop it back down with a little force. If a blockage is there this should break it. Not sure on your model but on mine the vent is a straight pipe clear to the tank. Let us know what you find.