Ring gear or starter ?

[Workuholic]

1978 w123
So I replaced the starter twice now in one year period
Still making screchening sound when engaging
Now its so bad that I had to turn the crankshaft manually for the starter to engage
So that tells me there is a worn spot on the ring gear
Is it the ring gear worn out or the starter neede shiming ?

[Diesel911]

Someone needs to get under the Car an inspect the Ring Gear.

On 2 different Vehicles I have had to file or grind down Metal Burrs on the Ring Gear.

Burrs (the metal gets pushed to the side and bulges making a high spot) for on the forward face of the Ring Gear. When the Starter Gear shoots out it catches on the Burrs but won’t go completely Forward enough to completely engage the Teeth so it spins.

It could also be that the height of the Teeth is gone but in My 2 cases getting rid of the Burrs cured the issue and you won’t know till you inspect.
Grinding off the Burrs is way easier than changing the Ring Gear so I think that makes it worth trying.

I don't now how much space available on a Mercedes to get at the Ring gear from under the Car.