there is no ufo on the 95 E300

the black line goes to the little unit on the injection pump that varies vacuum. Hard shifts are probably due to the points mentioned. i.e. perished rubber pieces on the vacuum line.

It is also a very good idea to have proper fresh ATF in there, it also helps a lot in proper shifting at low rpm. This transmission was tuned to take Dexron III or Dexron III-H (this is why mercon V works a treat in these later hydraulic shift mercedes boxes)

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)