Eaton 18 speed slave valve leaking air from vent

I think it’s called a slave valve. My range selector is sometimes slow to drop down into low range on the range selector. Not the side splitter switch. So I changed the filter regulator which was easy to do. While under there, I noticed that the other unit on the back of the trans is leaking air out of the little vent on top. In the picture is a red arrow pointing to the unit. Is this something I can fix or replace? I really have no time to drop the truck off somewhere. Tell me what to do please. And thank you for your time

 

I texted my mechanic the picture and asked if it was a simple swap out and he texted back a one word answer “no”.
I guess I bothered him this morning.
I don’t want to take it apart and run into a issue where something is complicated in there. I got to be at work tomorrow morning. So what am I looking at here to repair or replace this thing. Anyone ever worked on one of these? What’s involved?

 

What parts do I need to get?
I grease the ujoints weekly. They are all about 2 months old. I only put like 3 pumps in each one so they don’t fling grease everywhere. But someone else told me this week that I need to purge them. So I will do that today. This is my first truck

 

Thanks for the replies. All the responses I can get will be very helpful. I can’t have this truck down at all. I’m subcontracted for a large construction company with a dump truck. If my truck is down then someone else will take my place. It’s a 1000 dollar a day gig for 10 hours local. I’m a skilled mechanic and have built a few cars. Motors and all. I have never owned a truck or worked on these transmissions. I have all the tools. I’m actually working one mile from peterbilt so I’ll get the parts. I’m looking for any knowledge I can get about this valve. I didn’t want to get home from a long day and take it apart and have some springs pop out or something go all to hell where I run out of day light and have to call dispatch and tell them my truck is down becuase I decided to monkey with something the night before work. Maybe I’ll just get the parts and take it apart Friday night. What’s behind the box when I remove the 4 bolts. I indeed tried to research this thing and see if anyone has worked on it before posting but couldn’t find anything any where. Thank you for your time

 

How come this thing takes a couple hours to replace. Looks like just a housing and some orings that go somewhere