W123 Diesel not starting

[Grrrmachine]

Ive been offered a W123 200D for parts, which has been standing for the last six months. The panels are rotten, but the engine is good, it seems. It still turns by hand, and with a new battery on it all the lights pop up and the coils are warming, but the starter motor wont even try turning - no click, no whine, not even drawing more volts from the battery.

Apparently there was no problem with the engine when it was parked up, so I cant believe the starter has siezed - is there anything that could be a culprit here?

 

[Grrrmachine]

I can't see the edit button, so I'll add:

Shorted out the starter motor - got some fat sparks and a healthy whine, although the bendix doesnt engage: but it doesnt explain why it's not activating it from the ignition plunger.

Im really rubbish with electrics, so can anyone help me in terms of a walkthrough as to what to check for? It means the solenoid isnt activating, but I don't see why not

 

[Grrrmachine]

Did some electrical tests, and the glowplugs draw volts when you pull the plunger, but the engine wouldnt crack when you pulled further. I then tried to unscrew the two large cables from the solenoid, and that whole plastic end shattered and came off in my hand, so Im guessing it had perished to the point of inoperability!
I'll try and source a replacement soon - I'll update this thread just for people to keep track of the fix