Well, Sunday saw the first use of the new mash tun and no-so-new hot water urn. Big successes on both fronts!
The tun sealed perfectly, maintained good heat and had excellent flow with no blockages.
The hot water urn had none of the leaking issue that had apparently caused its early retirement, although the flow rate through the tap is a little slow. This means the lid of the mash tun is open longer and more heat is lost, causing difficulty accurately hitting the mash-in temperature. Might think about replacing the tap with a larger diameter ball valve, installing a sparge rig in the top of the mash tun, or possibly both.
But certainly as a trial run, I would be tempted to give it full marks.