Hey Ech!
Check the screw hasn't come loose at the bottom of the bracket, its a small phillips head screw which points upwards just under the key hole.then tighten the retaining nut behind the tumbler mechanism.
Let me know how you go, I am at home today if you get stuck I mite try coaching you through.I can post you my workshop manual and if you happen to have access to a photo copier you can copy what you want and post it back.
Cheers PAull