Did some chiselling…
In the first pic, you can easily make out a large fault line, the resin is cracked right through. I didn’t do that!
A nice sharp blow with a chisel, and this piece came right off, revealing the motor coil.
After lots more hacking, nibbling and chiselling, I got the motor coil out completely. That resin is damn hard stuff, and it totally encloses the coil.
I can see how it may have cracked though - it seems as though the motor coil "expanded" more than the resin and just pushed it o u t wards. (hot pump dumped into cold water - is 20°C diff enough to do this?)
The last pic shows some rust on the core so water obviously did get in!
After cutting the windings open, I found that the varnish insulation has completely "gone" in places, so this coil must have got very hot - for some undetermined reason…
Hence decision to measure new pump winding resistance to see how hot that one gets (copper resistance varies by 0.4% per °C)
edit: o u t ward is rude???