why do some turbos have vacuum line hookups and some don't. is it for an internal wastegate/boost gauge?

and when replacing an oil pan gasket do are you supposed to put something like rtv sealent on it?

 

Some turbos that are not setup with an internal wastegate have a port on the compressor housing. As far as the oil pan gasket goes, there are four spots you are supposed to put rtv sealant. It's kind of hard to explain, but if you find a FSM online you can see for yourself. Torque them correctly and you are good to go.