They are not the same but both will work on either motor. We put a w124 603 oil pan on my friends 350SD. Same bolt pattern but different oil capacity. W124 pan holds more oil because of the side-pan piece that bolts onto the main pan. Original 350sd oil pan has no side inspection hole on pass side. If it has that then the pan has already been replaced.

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'98 E300 Turbo "Juliette"
'85 Federal 300TD