I filled the reservoir up to the cold line and it has not gone down in a day hopefully it stays like that thanks. Do you guys know what the dome thing(picture) does?

 

I don't think my van even has one of those, but I'm still curious as to what it is so I hope someone else knows!

 

There is seepage all around the domed part, so I presume there must be some kind of fluid inside. Fluid wouldn't just sit there, so likely there must be hoses bringing the fluid there. Those hoses must be connected to something else which could offer clues to its function. Sometimes fluids can be identified by their color or smell, which would be another clue.

 

Maybe do a Google picture search using the image of the component. I initially thought the AC receiver dryer but mine is up on the firewall and not near the frame. The idea to see what hoses are going into it is a great idea too.