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s55 is direct injected so lack of fuel to back of valves can get gunky after while especially with the pcv pooping into the intake.
The cdi common rail cars had similar issue with intake gunk but due to egr dumping soot combined with pcv crapping oil vapor. Catch can should help along with reaming the car and avoiding short trips which don't allow car up to temp.
What catch can are you looking to get?
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