Newbie - advice re repairs to old Thomas Trackmaster trains

Battery corrosion is not a Tomy/Tomica problem, it would happen to any device that uses battery's especially left for 14 years. This even happens to batteries that are by themselves and not left in any device. As Leyland says above depending on the battery as the cheaper they are my guess would be the more prone they are to leakage but far any brand to be expected to last after being unattended for 14 years is unlikely. We have all learned a lesson the hard way. Good news for some is that rechargables are made much better so they don't leak but removing them when not in use is still the best method. As far as saving any of your trains with minimal corrosion, members here are always willing to help if you would start a Thread and post pictures with what you have. Getting your trains working again that you remember from your childhood would be great and I'll bet bring back fond memories of the hours you enjoyed playing with them

Yeah, I know it's an issue with anything where batteries are left, but I seem to remember it happening more when I was little, left for a month and they'd require cleaning. Other toys didn't seem to have batteries leak so often in!

Trying to get a replacement of this kind of battery terminalis very hard. So what you can do is solder a new battery terminal (the common ones with spring) with a wire to connect to the metal piece. If you need images let me know.

[Super]

That actually doesn't look too bad, Have you tried the White Vinegar and a cotton swab method yet or if you have a rotary tool with a little brush to clean up the corrosion? Also there may be some issues inside the motor unit that needs to be looked at to eliminate any issues inside like the switch.