i had the same problem couple weeks back, my brake pedal actually seemed as if it was gona fall of

so i took it to the garage and basically theres 2 clips/bolts either end of the pedal shaft and that one of my clips has come off causing the pedal to be wobbling everytime it gets touched
anyway they said theyve done this job before but for some reason the Si is the hardest one yet as there is literaly about a half inch for you to get the clip in there and THEN clip it in, if i remember correctly it took 2 days, but if this is the same case as yours then you really do need to get it looked at as thats "extremely dangerous and should not be road worthy in that condition" as they said.
hope that helps, ooh yeah its not even that expensive, only charged me a tenner for 2 days work

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