We all have to start somewhere!

Thanks for the detailed breakdown - I haven't had to do this yet but I do have a few non-working Thomas engines that I might try and get running now that you explained this technique.

Great care must be taken when first opening the two halves of the gearbox/motor housing, it's at this stage that bad things can happen, like springs flying off into another dimension.

LOL - I've totally experienced this with other repairs I have attempted. Somewhere there is a dimension that's just full of springs and other tiny parts.