Well, as far as a gasket sealer, I would NOT use any type of RTV or such. These provide a hard cure seal which can then be broken by heat and vibration - exactly the environment you're using it in.
When I did my Filter/Fluid change on my Tip S it was only at 25k mi., but the gasket was leaking. Since there is no dipstick for the ATF, there was no way to know what the level was at. Since I needed to remove the pan to replace the gasket, I swapped the filter and fluid while I was in there. See my DIY in the DIY section.
I used Hylomar as a sealant rather than RTV. Hylomar is a polyester/urethane sealant originally developed by Roll Royce as a sealant for their Jet Turbine Engines. It is a non-setting, non-hardening sealant and so is both vibration and thermo-expansion resistant. It is also a
zero-tolerance sealant which means that in some applications where you would need to account for the thickness of any sealant, you can use Hylomar and remain at factory specs - it does not alter spec tolerances. I have used Hylomar for many years and have never used RTV Silicone since - it works that well.
It was licensed to PermaTex, but I understand they now longer produce it as it competed with another of their products. But, Hylomar is available from Hylomar USA marketed as
Hylomar Universal Blue. At $28.50 for 100gm (3.5oz.), it's not cheap. But, you use very little when using it as a gasket sealant and 1 tube will last for years - it has an indefinite shelf life. Plus, used as a gasket sealant, it will NEVER leak again, unlike RTV, so that alone makes it worth the cost. See it at:
http://www.hylomar-usa.com/
Also, the Durametric will not activate the OBC, only a PIWIS or PST2 can be used. My dealer did it for free when I had the car in for some other work. Others I have heard have charged $60 or $100 to do it while still others have outright refused to do so. Seems the best tactic is to ask them to turn on the temperature display, never letting it slip that you're planning the OBC Hack.