Any of the Gasket sealant RTV's will work fine, so will ordinary bathroom RTV. From a practical perspective, there are really only three basic types:
Std (smelly)
low VOC (expensive, use in aerospace apps a lot)
and High temp for exhaust and other high temp uses.
I think the RTV II for exterior construction use may be somewhat different as it's made to not sun-rot.
After that it's all about dyes and marketing.
I've actually used bathroom RTV on engine gaskets with no issues. (white looks a bit odd if it shows, but it worked exactly the same as Permatex RTV for ordinary gasket use...)