well what should do about the drive train then i have 2 gear the need to be in there though since i can put a new gear on the axleI think the clue is in the question - your post #5 says the gear is toast. I think you have to ask the reason why.
Large scale locos end up doing quite a bit of work, and the drive trains take the brunt of it.
The way that I'd be tempted to approach it would be to try and obtain a gear wheel with identical properties (number of teeth and axle bore) to the knackered one, and do the simplest like for like replacement and see whether the loco can cope with the demand.well what should do about the drive train then i have 2 gear the need to be in there though since i can put a new gear on the axle
Sound realistic advice.If the loco in the first picture is what you are working with then my advice, which come from experience with one, is keep the body and throw the rest away.
The drive is that weak it could not pull the skin of a rice pudding and will fail under a heavy load which is what has happened to yours.
Look for a economical motor block and put that under it.
I put a USA trains block under mine and it worked fine, I later carved it up and used the parts as the front for my railcar, the other half is an old LGB coach.
Edit: If I remember correctly the guage is not correct for 45mm track either.
View attachment 290882