Thunk

You know you are going to have a bad week when you sit down at your office chair of a morning, lean back to hear a "Thunk" at which point your chair, rather than sitting at the locked tilt position proceeds in to the full lean-back position. 
Resetting position, fiddling with the many levers on this chair don't work. Inspecting the under-carriage of the chair to "see" if you can work out the issue and what falls out - this chunk 'o' metal. I was unable to check the internals of the tilt mechanism - turns out - it's not a serviceable part as it's put under tension in the factory. This I believe is half of the locking pawl that sits inside this mechanism. Sheared in half. 
Now I have to contend with my chair trying to push me out of it now, or sit in a laid back position with no middle ground to lock the chair into. This is going to be fun to fix, or replace.