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I decided to pull master cylinder and disassemble /clean it.

I took off the circle clip on the end - and i pulled the stop screw on the bottom - but I can't get the cylinders to come out... the shaft pushes in fine and seems to hit a "stop" when released...

What am I missing?

I disassembled mine this winter, it did take some effort to pull the assembly part.
I was not shy at aggressively pulling since I decided to replace it with new. It was
more of a curiosity why the front Master failed which turned out to be due to a deteriorated
gasket. Before I took it apart I did notice tool marks on the shaft indicating this had been
apart once before, my guess would be in ~2000 when she was completely overhauled.
Made me think twice about where to source rebuild parts from, this should have last
30 years not 15

IMHO get a new one, esp. since they are readily available, rebuild this one as a backup,
for that day they ain't all that available. Get your rebuild kit from EI if you want 100%
assurance it's OEM. My $0.02

Thanks - My plan is to replace it - mostly just wanted to see the condition and if it was rebuildable as a spare.

I'll go at it with some tool on the shaft. I suspect there is corrosion inside anyways. there is a sticker on the booster saying it was replaced in 1993 - which is when I think my pinz was rebuilt by the swiss.

I'll be ordering a new one from EI for sure tomorrow.

oem part info

the master cylinder is the same as the mercedes /8 series and can be rebuilt with the ATE kit RK2371

Compressed air should push the piston out

I got the master brake cylinder apart finally - and I found the internal stop bolt (#9 in the drawing) was loose inside of the cylinder bore - which then caused the shuttle piston (#15) to stay in a part way depressed position since the spindle piston compression spring (#8) was not properly restrained by the bolt and was instead pressing against the shuttle piston all the time, keeping it from moving properly.

This explains why I was getting weak braking and was not able to get any flow out of the front brake chamber when I tried to bench bleed it.
I examined all of the seals and the bore and they all look to be in good condition so I am going to reassemble it (correctly) and will give it a try.