Out with the angle grinder, off with the bolts head, tap an old knife blade into the clamp to open it, bit of wiggling and a gentle lever with a long tyre lever and the exhaust is off.
Now for the swinging arm pivot, this’ll be a swine, it’s never been out before. Undo the pinch bolts, rubber bungs out, give the drift a gentle tap and IT MOVES!!! A few gentle taps and the pivot bolt is out.
Lift the arm and shock onto the work top. A touch with a strong magnet and the broken bit of allen key is out – too easy.
Grind the remains of the key flat and try again, ooh, that’s in tight, going to need a longer lever. Give it a spray with penetrating oil and go for a coffee. Took a serious effort with an old fork stanchion on the allen key to get it to undo.
Hmm. Bolt is well corroded.
The bit of bent metal sits in a groove in the arm to make the nut captive, also means you can’t get a spanner on it to undo it.