What I did for my Reatta today: Started the thermostat replacement ordeal. An 11mm crow's foot on a 3/8" drive universal joint and extension, or a 1/4" drive 11mm socket with a 1/4" universal joint and extension are needed. It helps to unplug the vacuum hoses, being careful not to break the plastic manifold fitting (oops...).
Parts needed: the thermostat, obviously, but also the following two Fel-Pro parts:
Fel-Pro 35608 Engine Coolant Thermostat housing O-ring
Fel-Pro 35126 Engine Coolant Thermostat Seal
I found both on Amazon, neither of my local auto parts stores could source the seal.
BTW, I don't understand why folks replace their OEM 195 degree thermostats with cooler units. The engines run more efficiently at higher temps, as long as they were designed to function that way. You are no more prone to overheating with a hot thermostat than you would be with a cooler thermostat, or even no thermostat at all. The ability of your car to avoid overheating is determined by the health of your radiator/fan/waterpump setup, along with the degree of corrosion buildup in the cooling passages. Let her run at design spec, those engineers had good reasons for doing it that way.
As for the engineer who decided the thermostat housing retaining bolt needed to be nearly inaccessible with standard tools, that's a different story! May he/she be destined to have to access basic necessities on a regular basis with a similar level of frustration!