Andy
Forgive me if you know this already, and this may be a red herring.
If you have a copy of "Laurence Meredith, Original Mercedes SL, The Restorers guide to 300SL, 190SL, 230/250/280SL models to 1971”, there are a couple of interesting pictures.
For want of a description,
Your 230SL has a Long body Booster with recess for the master cylinder.
My 280SL has a Short body with no recess for the master cylinder, see picture.
In LM's book the reference photos are the other way around:
Page 82 shows a 230SL with a Short body with no recess,
Page 86 shows a 280SL with a Long body with recess for the master cylinder.
This sort of indicates both our cars have the wrong ones, and could explain the issues you faced with clearance.
Perhaps others can comment on this?
Out if interest, my booster was replaced in 1983 at cost of £147 so they were expensive then!
Peter