I went through this ordeal a few months ago.

The piston kit is available but expensive.

The kit with the valves and rubber bits is NLA.

Your best bet is to find a shop that has NOS, or ebay.

I even checked with the MB classic center and they couldn't get that kit.

keep looking, or like mentioned before, buy a rebuilt/new pump for a little more.

if you do find the kits, the rebuild is easy.

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1983 300CD Turbodiesel