As is traditional for me (don't start), a routine disassembly becomes more complicated as a result of a sheared bolt. Removing the water pump for inspection, it was the centre top bolt - with the thread exposed at the back, so likely corroded in. The good news, the bolt sheared just below the hex, so maximum bolt length to remove the stud. The bad news, the bolts are threaded for their entire length, so I can't get the pump off due to this one sheared bolt.
The bolt seems to be an M8 flanged 30mm. Lrcat talks about M8 but 25mm - I doubt it matters greatly, but I just wanted to be sure I had the right spec, anyone know?
I'm hoping that when I get the water pump off I find that the impeller is on its way out, which will make me feel better. There's definitely some play in the bearing, so that's good.