It is the factory setup, although they only used this particular design on the 75 & 76 300d (It's a great car but there are enough differences from the w123's that finding certain parts can be troubling) Besides there is no provisions to mount a primer on the injection pump. (that is where they mount on the w123 right?)

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'84 190d 2.2 - Silver
Converted to 5-Speed
'84 190d 2.2 - Blue
Factory 5-Speed

'76 300D (W115)
Sold, found again in less auspicious circumstances