Unless you buy contaminated fuel (see the "buy your fuel from a different source" suggestion above) I wouldn't bother until its time to change the filter or you can see water in the bowl.

Anyone have the pictures for this thread?

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1985 300D (CA, 173K)

Dynamite Biodiesel Co-op, Phoenix,AZ

If you do a Google Images Search for the Stanadyne FM100 you can see what it looks like.
On a 123 there is space avaliable between the rear of the left Head Light and the left Front Fender Well to mount something.

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84 300D, 82 Volvo 244Gl Diesel