Michael did not swap the entire manifold, but did change out all the valves and coils. What prompted the replacement of the valves and coils was a failure of the third one down (or the third one up) because the bus would not go into the driving height position.

His vintage coach is on the cusp of having other suspension system components begin failing and now has some problem with leans so he will soon replace the air bags, and I presume the norgren spool valves.

I recommended that because when a bus reaches the age of his the original components are near the end of their life cycle based on the numerous bits of anecdotal evidence that has been posted here over the years.