EPCnet Online the official Mercedes-Benz USA, LLC site for hosting spare parts documentation for Mercedes-Benz cars and light trucks sold in the USA seems to designate it as the "PRESSURE CONVERTER". Item no. 941 Part number
A 123 300 11 33. In case someone is getting blank stares at the parts counter.

One wonders if a retrofit of this item on pre '85 diesels is doable and worth the trouble.

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'83 SD, 2x '85 SD
You are entitled to your own opinions, you are not entitled to your own facts.