The ZF41.be site is a very good source information. There's a site for ZF41 and other German WW2 scopes in general
http://homepage3.nifty.com/zielfernrohr/index.htm
and another one depicting the guts of the ZF41
http://www.k98k.info/index.php?p=showtopic&toid=402&fid=38&page=1&t=zf41-vs-zf41-1
A word of caution: The ZF41 reticle appears to be silk screened or printed onto the center lens and is extremely sensitive to the touch: You clean it with alcohol or lens cleanser, it comes off. You lightly rub it with a soft brush or a Q-tip, it comes off. Either way you lose big time, so DON'T mess with the reticle. Leave it to the experts. If you over estimate your skills, you can quickly turn a $400 scope into $100 parts donor. You simply won't find a spare reticle!
I recently picked up an original dow ZF.40 (factory upgraded to ZF.41) with original mount at the gun show. Price was OK, in the order of what they go for on feeBay but I was able hold it in my hands, look at it and check it out before I dropped down a wad of green.
Like almost every dow scope I've owned so far -be it ZF4 or ZF.41-, the grease had solidified and its evaporated oily components had fogged up the lenses. Disassembly was a bear due to the solidified grease but warm air from a hairdryer helped a lot. Luckily, I only had to remove and clean the front lens assembly to make it clear and movable again. I bore sighted it and took it to the outdoor range the other day.
With some minor adjustments (once you figure out how the two adjustment pins move the lenses around, it's actually pretty easy) I walked the point of impact right into the bullseye and shot nice 2" - 3" groups at 100 yards afterwards. I'm still getting used to the ZF.41, there's definitely room for improving the accuracy. The rifle I used was a bcd 43 with the bogus rear sight mounted "sniper" rail sold by Numrich.