A general problem is that the Dianas with double piston system (designed by Kurt Giss late 50's), are a little tricky to repair, when the old cork seals are worn out. Sending them to a gun smith will cost a lot. Dianawerk in Rastatt charges about 180 Euros for a repair, which is about the same value as the gun itself (or more).

I have replaced selas and springs in a few (pistols and rifles), and think it is sad to see these fine pieces of air gun history being thrown away just because they are tricky or expensive to repair. The only manual from the factory, for Diana 75, is in German and is not very accurate or detailed.

I live in Sweden and have written manuals (MSWord format) for how to repair these guns.
This manual is in english for Diana 60, but will work to 95% for models 65 and 66 too.

Manual for Diana 75 in swedish. (sorry, I'll translate it to engish some day. There are pictures and stuff you might find useful.)

Manual for Díana 6G air pistol (swedish too....)

If you are interested in sales statistics and prices for old match guns, including the Dianas, I have collected them the last three years from egun.de at this link. This file is updated weekly. File format is XL, and there are some 2500+ prices.

/ Micke