Yeah... it's not looking good.
Motor housing is full of fine sand / mud and it's all corroded inside.
2/4 Brushes are seized within their holders, and the rotor has some significant rust and light scoring in the area where the brushes wipe over it due to all the sand and mud that was inside it.
I'm going to have a crack at the 'repair' option, but this might end up being a 'replace' the 12V motor assembly job. We shall see.

