nEED HELP DISASSEMBLING 944 BRAKE MASTER CYLINDER

[100forks]

I Have A 1988 Porsche 944 base model., with a Girling brake master cylinder that I can't disassemble. Markings on the cylinder are 114/13 and 0852. It does not have the top or side stop screw. I removed the circlip and then the small stop pin located in the rear reservoir hole but I cannot get the piston assembly to come out. It appears that there is some sort of a brown colored collar (at the front of the cylinder), which I have tried to remove with needle nose pliers but it will neither come out or rotate. What do I need to do to finish disassembling the cylinder? Thanks.