So I found this listing: https://www.ebay.com/itm/326303073805
...it would be one way to get a DPU-40 manual, I suppose. I contacted the seller, asking if they could photograph the manual for me; I don't expect much of a response, but I've been surprised before in the past (most recently with a manual for a very old Dremel moto-tool from the 1950s)...
Still looking around, though - I'm kinda like "a dog with a bone" on these kinds of things...lol.
Andrew L. Ayers Glendale, Arizona phoenixgarage.org github.com/andrew-ayers
