We replaced my brake booster hose (y pipe under plenum) with an updated aluminum and silicone hose assembly. It is made here in AZ by a local M5 owner, the old hose asembly was brittle and not sealing very tightly on the metal pipes.
While the plenum was off we cleaned the throttle blades, lubricated the throttle linkage, and addressed other small vacuum hoses.
While the plenum was off we cleaned the throttle blades, lubricated the throttle linkage, and addressed other small vacuum hoses.