All,
Well, we've all heard if your Electrical solenoid doesn't work then toss it and find a new one. Thanks to the generosity of Bookwus (Mike) I had a sacrificial lamb to conduct experiments on.
After a session and a "minor industrial accident" on the lathe I got to here :
(http://i40.photobucket.com/albums/e210/ctefeh/VWControlValve/SolenoidDis.jpg)
You can see there that there is a "hat" that your wires connect to (more on that later) and this in turn is held into position by the crimping of the steel body against a rubber seal (that wonky looking ring). The ring at the top left is under this "hat" and is held on by the central brass tube being flared flat. Careful work with a small chisel raised this enough to take the ring out. It sits in it's own little recessed section of the steel body. The plunger is steel and quite a heft little number. The tapered portion has a matching section down inside the brass tube.
What's left is the solenoid winding capped off by a bakelite (or phenolic material) disc and wrapped in the finest german brown paper bag ;D . The two wires have cloth insulation where they poke up out of the disc.
So onto the "hat"
Underneath it's like this :
(http://i40.photobucket.com/albums/e210/ctefeh/VWControlValve/Solenoidhat.jpg)
You can see two little rivets separated by a bakelite/phenolic insulating strip.
Melting the solder on the top freed the wires and I drilled out the rivet "flares" and it all came apart like so :
(http://i40.photobucket.com/albums/e210/ctefeh/VWControlValve/SolHatDis.jpg)
Pity I did that after I'd sliced the top off :(. At least I left enough wire available to fix it up before I attempted to slice the bottom off!
The rivets are held off from contacting the steel "hat" by rubber insulating sleeves. And check out the corrosion that was between the plastic top section and steel "hat" body. In the first photo it appears to have leached inside.
I'd say after having a look inside that the actual solenoid section is pretty solid and straightforward. The corrosion is a bit of a worry and also the sealing ring from the first photo. Grab that non-conductive sealant and slather it on good and proper!
As for repairing one...well depends how desperate you are and how much you really want to fabricate. Once you slice the top belled section off the steel body you are left with "how do I seal it all back up?".
I'd be making either an interference fit ring with a fat o-ring groove in it, or a stud set-up to bolt one onto it. This assumes your cut is spot on and you've unsoldered the wires from the spade terminals.
Enjoy
Volkenstein