The Meccano E6 motor dates from an age when things were made repairable. It is mostly screwed together (of course - it's Meccano) and comes apart easily.
(The notion that you could make an expensive consumer product and explicitly design it so that it is near-impossible to repair was probably not yet mainstream.)
After disassembly and cleaning, this is what we've got:
The brass was only cleaned (soapy water) and not polished, except for the electrical contact surfaces. Decades of patina increase electrical contact-resistance and will slow these motors down or prevent them from running at all. Normally not visible, the switch-contacts are now brightly polished.
Nominally it is a 6 Volt motor, but by the look of the area around the brushes it may have been used at higher voltages, would not be surprising if a previous owner ran it at the 20 Volt that later Meccano motors needed. Not only does it look like it sparked fire, the commutator is also visibly worn down.
Now that they're clean, the fading of the paint can be seen very clearly from the difference between inner and outer face of the side-plates.
Were it not for the nicely surviving decal, these would be up for a re-paint. Maybe later - first to make it functional again.
The bent lever of the switch was easily corrected - protecting the part with card, holding it in a vise and use parallel-pliers to gently 'form' the bent bit. (From typewriter-repair; 'forming' is bending when you mean to do it.) The brass pillars that hold the laminations likewise needed some straightening, probably more tweaking to come.
Up next; find a way to build-up and fix the broken black switch-base.