If your car requires a cut out thermostat to run cool then you have some other problem that has had a band aid put on it. Aonther thing, a compression test will not diagnose a "seeping" head gasket on a Legend. The next few things are ways that I have diagnosed leaking cooling systems and blown head gaskets on a Legend. I am ASE master certified and have been for a couple of years now, so you can trust this information if you want to. I would print this out and take it to your shop.
Pressure test the cooling system for leaks. You may actually need to squeeze the smaller hoses on the throttlebody, oil cooler (if it has one, some do, some don't), fast idle valve, differential cooler, and heater hoses. I have seen them hold pressure and when you squeeze them small pin hole leaks appear.
Have a block test done (the turkey baster looking thing with the blue liquid inside). If it passes then proceed to the next step.
Have a leak down test done. This is what I have done and it was successful on 3 of my customers Legends as well as my 2. Directions are as follows.
1. Remove the radiator cap. Make sure it is full to the top with coolant. If you have an eazy fill funnel that attaches to the radiator fill neck use this half full of coolant. Leave it like this as you are going to look for bubbles. NOTE you don't want to see any. If you do this means you have a BHG.
2. Insert the compression tester spark plug adapter inter the 1st cylinder to be tested.
3. Connect shop air to that adapter hose and fill the cylinder with air. You may need to use a pull handle on the crank pulley bolt to turn crankshaft so the valves seal off the combustion chamber.
4. Once it seals off watch for bubbles as you turn the crankshaft slowly until the valves open again.
5. Repeat this on every cylinder.
If that doesn't show any indication of bubbles then you most likely do not have a blown head gasket.
Another reason a cut out thermostat could be used is if the radiator fans are not working properly. Maybe they are spinning, but worn enough that they are not moving as much air as required to cool. Another thing is to flow check the radiator. The best way I have done this is to remove the radiator and pour water in a radiator hose connection and see if it flows out the other side with the same volume. If not then replace the radiator.
Hope this helps...