I'm replacing the radiator and thermostat in my '91 Nissan 240SX and
have a couple questions:

For the thermostat, Nissan says to just use liquid gasket
(silicone/RTV).  However, several auto parts places sell a flat gasket
part for this application.  Which is better, the liquid gasket or the
flat gasket part?

Some places sell a single model of radiator for this car, whether it's
a manual or an automatic transmission.  Such radiators have connections
at the bottom for automatic transmission cooler lines which can be
covered with rubber caps.  My car is a manual trans.  For my car, would
a radiator with the auto trans connections be a potential place for
leaking to occur, and would it therefore be a bad idea to use such a
radiator?

Thanks for any and all advice on these topics.

M.