Agree with identification but disagree with the solution. If this is on the firewall, I believe that is the switchover valve which often becomes clogged and needs to be replaced. Be careful to note which rubber hose goes on which nipple. On my SD I reversed them and the vehicle would hardly go over 30 MPH. Looked at the manual and corrected the hoses and immediately got original power.

If I remember correctly the new switchover valve (original was 1981) was upside down from the original which is why I got the hoses misplaced.

It is there for a reason; trust the MB engineers.