Hey Bob,
No gasket, just use the o-ring that comes with the new thermo. If the bolts have'nt been off in awhile, they can be a challenge!
The bolt that is under the injection lines that has the slot in it, can be started using a good screwdriver (clean edge, not rounded). You need to get a good grip in the slot so that you dont ruin the slot edge and loose the grip. I think I used a screw driver with a good pair of piers to assist in the initial few turns. I then used a wrench. Next time I will use the new ratchet box wrenches that I rec'd for Fathers Day. These new wrenches are really cool!!!
Also, not sure if this was a good thing to do... but before I re-installed the bolts, I smeared a bit of anti-seize paste on the threads. Dont forget to "burp" the system and get all of the air out. With air in the system, the engine can overheat. I usually park my car on an incline, front higher than the back. After replacing the fluid, start the engine and look inside the over flow tank. When the car reaches the point that the thermo opens (ie 79c), you will see a big bubble, burp, and the air is then out of the system. I also made the mistake once to change the fluid when it was hot. It is better to change it when the car is cold.
Another thing to remember is to ensure that the thermo is positioned the correct way. The small "floating bearing" on top of the thermo needs to be positioned at the highest point. Usually positioned towards the front of the car. This is how the thermo releases the extra air in the system. The air escapes from the highest point...
Bob
bpossel
Memphis, TN.
1971 280SL
1997 E320