Car appreciation... the aesthetics, the engineering, etc

Anyone have much w203 knowledge?

Got a C220 cdi here which was starting about 1 in 30 clicks of the key. When it does turn over it goes at normal speed. Battery and charging system seem healthy.
Prev garage diagnosed a bad starter and solineoid.
Got a new one, works on the bench fine, but in the car just clicks forever no turning over at all, not one single movement.

At key turn you get three clicks, steering lock relay, starter relay and solenoid clicking pretty healthy.

Still blows it's #52 fuse every so many key turns.

Suspect bad main earth strap but can only find the gearbox one (which is rotten), engine one no where to be found. Any one know? Or other w203 starter issues?

Update. Sorted.
My theory, bad worn starter and mercedes undersized solenoid trigger wire (they blow Fuse 52 all day long even when working properly) has melted some part of the positive main feed (1/2" monster cable) and it has very high resistance. On this car the starter motor gets its positive feed not directly from the battery or distribution terminal but instead via the bottom of the alternator? So there is nearly 2 metres of cable going from battery, to distribution, then to alternator and then back across the engine one last time to the starter, no wonder it broke! The battery to the starter is like 40cm.

So tried all sorts, couldnt' find the break without taking the whole damn car to pieces, so have put on a monster beef cable taken from earth strapping from an industrial control panel, wrapped it in a couple of layers of inner tube then precision threaded it direct from distribution terminal to the starter. That way it least has the big 250 amp main board fuse to protect it incase it goes south. And with the new starter, starts like a boss.

Now just have to fix the rampant black death on cyl 3 (injector is pushed out/bad seal but also not easy to remove, need a big slide hammer on it).