Right. After first install I was losing coolant after driving it for a while. Brought it back to the mechanic and watched him fix the problem. He put the car on the lift, drained the coolant, pulled off the intake tubes, undid one side of the oil lines, pulled out the t-stat housing, pulled out the coolant tubes from the block, replaced the broken o-ring, inspected the rest, lubed everything back up, and reinstalled. Total time was about 30 minutes of work to fix the leak. After watching him do it, I'd feel confident tackling it myself if I have to replace the thermostat again. Sorry to derail the thread slightly, OP
