The W201 FSM is available on startek for free now
The steering chapter (46) is here =>
http://www.startekinfo.com/StarTek/outside/11832/Resources/201Create/PDF/10011.pdf
No mention of the alloy casing though...
...I'm going to have to bend the ear of the head mechanic at the dealer - or perhaps get access to WIS...
...as for the adjustment.
I found it tricky on both the W123 steering box and the W201 steering box to adjust.
You tighten the screw in an anti-clockwise direction and check the torque as you turn the input shaft through its central position. If you over tighten it and then nudge it back a bit it seems to loose its place. It is weird - you would think oh sheet just turn it back and it will be back to where it was - but it isn't. It like there's some form of hysteresis in there (or summit like that).
Strange.
To get back to where you were I think it is necessary to back off all of the tension in the adjusting system and start again.
So I advocate a policy of not messing with that little screw. I think nipping it up is likely to bugger it up...