A little while ago, I managed a great deal on a vintage Kaweco V12 and 619 set from around 1965. It was a bit of a risk, bought it on eBay with only one picture so didn't really know what condition it was in. Fortunately, it arrived and when I started to clean it and take it apart it turned out to be in VERY good condition and needing nothing other than a cleaning and some silicon grease. I've done a review of the pens here.
However, between winning the auction and getting the pen, I was looking online on how to restore them, I was worried it had a cork piston seal, I couldn't find much. When I couldn't find one, I thought I would take some pictures of the steps as I did it to my new pen, so here's a quite guide on how to take apart a Kaweco V12 and what the parts look like.
To start things off, here's a picture of the pens and the case as they arrived.
The first thing I did was soak the pen in some deionized water for a few hours, pulling it out of the water to let the water inside the pen drain out and then refill the pen. This washed out virtually all of the ink, which turned the water blue likely meaning it was a washable blue ink that was in it.
After the water coming out of the pen stayed clear, I used some nylon pliers to pull out the nib and feed from the pen, which come out as shown below. They just pull straight out, if they don't come out easily, I'd suggest soaking in some soapy water maybe then applying a little dry heat (not too much, the pen is celluloid). The nib may come out by itself without the feed, if that happens just pull the feed out with some rubber tipped pliers.
Once removed, this is what the nib and feed look like. They can/should be soaked by themselves in clean water just to make sure everything comes off them, could even give them a gentle brush with a toothbrush to make sure.
While I was soaking the nib unit, I started on the piston. On the pen, the seal and piston had come loose from the nob and twisting the nob at the back didn't do anything to the piston, which had me a little worried. When I was looking at the threads, i thought they looked a lot like the threads on a Parker Vacuumatic, which I have the tools to remove. So I grabbed that and it was a match. However, as soon as the unit started to unscrew, I realized that using section pliers are a better option. You can see from the photo below, that the piston unscrews from the barrel of the pen at the metal o-ring rather than at the nob. This means that the piston forms part of the barrel at the top of the pen. This makes using section pliers on the back end of the pen the best option for removing it. My pen didn't have any shellac, but I can see some pens might, so not a bad idea to apply a little dry heat, again, not too much.
(this photo is actually from putting the pen back together, that's why the piston isn't sitting in the ink window).
Once out, I could see why the piston had come loose from the nob. It's different from the TWSBI piston units as there's a screw that's attached to the nob which fits into a threaded hole inside the piston. There is a square hole in the nob piece which the piston fits into to stop it from rotating and the nob turns a screw which extends or retracts the piston. The below shows the pen fully disassembled.
To reassemble the pen, I started with the piston. I put silicon grease on the seal to fill the notch and all along the sides of the seal. I also put grease into the hole in the nob unit, on the outside of the piston shaft, and on the threads that screw into the barrel.
I then put the piston into the nob unit and fully retracted the piston. I then screwed the piston unit into the barrel of the pen. I only finger tightened the piston unit as I didn't want to crack the barrel of the pen and was confident it wasn't going to come loose. I wouldn't recommend using section pliers to screw it in as you might over tighten and crack the barrel. You could apply some shellac to the threads to keep it in place, but I didn't want to and the fit is good enough on my pen that I wasn't too worried. The pen is much easier to thoroughly clean if I can remove the piston.
It was then just a matter of putting the nib back onto the feed and sliding it into the pen. It goes in smoothly and there is a final little bump you can feel it go over telling you it's in there securely. Because of how the nib fits onto the section, it's very difficult for it to be misaligned, but always worth a check as once on the pen it's difficult.
After putting it all back together I tested the piston with some water and it worked great, so inked it up and gave it a test and been very happy ever since.
For the 619 ballpoint, the pen came with a refill in it, fortunately, but it had long dried out. I was able to find out that the Schneider 75M refills fit the pen and ordered one black and one blue.
To remove the refill, the front of the pen simply unscrews.
As you might be able to tell in that photo, the Schneider refills are a little too long for the pen and need to be cut down slightly. I used the refill that came in the pen to get the correct size, unfortunately I don't know the length of what I cut off, but it's around a half inch I think. There was a bit of foam in the piece of the refill that I had to cut off, so I pushed it out and put it back into the back end of the refill to stop it from drying out. I then rounded off the corners a bit and put it into the pen. Worked great and writes very well.
The click mechanism is a bit unique. To extend the pen, you push the button down halfway and it will stay there with the pen extended for use. To retract it, push the button the rest of the way and it will go back in. This means if you push the button all the way down in one go, it will extend then retract the pen in one push. This took me a couple of tries to figure out and I think would catch your typical ballpoint user off guard, they are likely to think it broken so if you let someone borrow the pen, best to explain. You can see in the below, the pen extended and the button half pushed.
Hope that was useful to someone and if you get a chance to get one of these pens, I'd highly recommend it, they look to be very low maintenance and rather easy to restore if there aren't any broken pieces. Again, you can read my review of the two pens here.