Find and fit a servo and all will be normal again.
The servo had a boost ratio of 1.9:1 on yours i believe, in other words, for every one pound of pressure you push the brake pedal down with your foot, 1.9lbs of pressure is fed into the master cylinder :
https://www.skandix.de/en/documents/...tions/3000118/
Some instructions there and i daresay you can find the servo (aka booster) on skandix too although likely to be ŁOUCH! compared to a secondhand unit from a helpful forum member or similar.