Bob,
the CSV is a simple beast and well worth attempting a fix yourself, in my opinion. It may only need a good cleaning, that has saved more than one. The term ball-and-spring may be slightly misleading, an artifact of translating German terms to English. We'd probably call it plunger-and-spring(?).
The solenoid can indeed get stuck, in my case the rod was stuck to the tiny rubber seal. A bit of WD-40 and some twisting/pulling/pushing in/out freed it up.
My valve was also stuck. After disassembly and pushing the plunger out, I cleaned the valve bore with a roll of fine emery cloth soaked in WD-40. The pressure of the roll trying to expand outward was enough, you don't need a lot of pressure. The idea is not to remove metal, just whatever varnish or lead or whatever is stuck to the bore wall. Anyway, move the roll in/out and twist it a few times, then trial fit the plunger. Keep at it until the plunger is free but doesn't wiggle side to side. Also clean the valve seating surfaces with a good carb cleaner or similar on a Q-tip. Reassemble and give it a try. You're only out 30 minutes and no money if it doesn't work, so what the heck. If that doesn't work to seal the valve, then lapping would be the next thing to try.
Easiest to work on by removing the CSV from the manifold. I found the large o-ring seal at a plumbing supply store. There might be a paper gasket, too, but my car didn't and still doesn't have one, just the o-ring.
Good luck!
George Davis
'69 280 SL Euro manual
