Had same on my secondhand 453. I bought solenoid from Smart / Mercedes £94. But the lower part that goes into the engine block was well siezed in. I couldnt get it out. Took to dealer, took them two & a half hours to do what they said takes half an hour. Cost £211.
mate that’s extremely cheap from a dealer £94,from which Mercedes was it?
Yes there is build oxidation like white salts builded around it, it is a chemical reaction resulting from aluminum and steel contact.
all I did was remove the 8mm bolt that holds the solenoid, and spray little bit of WD40 around the solenoid(there is a tight rubber gasket in the solenoid so no fear from dropping inside the engine ) let it soften those white salts for a minute and then wipe it with a clean microfibre and kindly rotate the solenoid before pulling it up,then wipe again making sure nothing can drop in the engine while you re pulling it off.
by rotating the solenoid the little ear (the one that the bolt goes in to hold it in place)is breaking loose all those white oxidation salts and they even become like a white cream (because of the wd40) easy to whipe.
that way it rotates freely and you can gently pull it up.
total time :15 minutes