I have a 1991, 2.0L, 3S-FE Camry. I have to replace the radiator and it's leaking antifreeze from where the water bypass pipes bolt in to the thermostat housing.

According to a diagram I got from the dealer, 2 10mm nuts hold it to the housing, and then there are 2 other bolts(12mm) holding it. I undid the 2 10mm nuts and the 12mm bolt right before one of the pipes connects to a hose and the other pipe bends and goes to god knows where. I tried prying the pipes loose at the housing, but then got the feeling that I was about to break something that I really didn't want broken so I stopped. Is this other bolt what's keeping it in place? Where is it? I couldn't find it.

Also, the repair manual at the library said that there's an o-ring and a gasket for the pipes. The dealer said that there's an o-ring but no gasket and that they use silicone instead. Does it matter?

If you face the engine from front of car, the bypass pipe bend 90 degrees toward the rear of the car. There lies a bolt secure the pipe to the side of the cylinder head. Just follow the pipe closely after the bend, you will see it.