The bottom of the regulator is probably a water filter/separator.The bottom fitting is a drain. Some unscrew, some have a ball bearing in the bottom you push up, etc. You can remove pressure and unscrew the bowl to get a better look at it. Most are just 1/4 tunrn to take loose. Only maintenance here should be draining the water out of the bowl, using the bottom fitting. If the bottom fitting is leaking, then all the water gets out on its own. You should be able to buy a replacement bowl with the bottom fitting if you can't get it to stop leaking. You may also be able to get a new fitting only but a lot of them are integrated into the bowl.
Is the red line the incoming air? I'll assume it is.
I'm not sure about the other component. It could be a vortex separator. You see how the inlet is offset, that makes the air spin so chunks of crud go to the outside and fall to the bottom rather than going into your regulator. If thats what it is, it might be good to take it apart periodically and clean out the crud. If you have clean shop air, then you will never have to touch it.