View attachment 61447 View attachment 61447 View attachment 61448 Hi This is the first time that I have tried to post a photo, apologies, if it is not correct. Hope you can see enough either on thumbnail or full size.
That brings back memories!
Those motors compared to modern ones are like comparing a Morris Marina with a modern day Audi A4...
Good in some ways though as you wouldn’t even attempt to fiddle with stuff under the bonnet of an A4 (mainly because you wouldn’t have to), but a Marina is simple and you can see what everything does.
The old Hornby motor comes apart quite easily, but I still think you need to check the easiest stuff first - namely the lead brushes that rub against the commutator (I hope that this is the correct terminology).
Lift the two silver tabs up on the side of the motor that doesn’t have the brass gear wheel on it, and be careful not to lose the little springs behind the tabs that push the brushes onto the commutator (again do this on a tray or something similar to keep the parts in one place. Use a cocktail stick for the springs).
If the brushes are this shape:

Then they’re fine.
But if they’re this shape and are getting wedged between the casing and the commutator:

(Sorry about the poor quality drawing) Then they’ll need to be replaced.
The reason I’m suggesting looking at this first is that it’s always best to check the simpler consumable parts first before stripping the whole thing down.
Have a look at this first, and if it isn’t that (again, post photos of what you find, because it might help us work out what’s what), then we can look into it a bit deeper.
I’ve repaired plenty of these motors over the years, and it’s usually something fairly simple that’s easily fixable.
I had a pair of permanently coupled class 25s for a while that had three of these motors between the two locos. I through wired them so that they didn’t stall over points and they ran like an absolute treat.

A spray can of switch cleaner always helped mind - Available for a few quid at Toolstation (other local DIY wholesalers are available).
Don’t be frightened to have a go at fixing it though.
It helps to have a few spares in a box and to be able to swap bits around until you get it working properly though sometimes...