I got the Bachman's Big Hauler #90-0100-27 out of the attic in hopes to surprise the grandson. The train has been in the attic for 20 years. I put new batteries in it and it failed to run.  It had been stored with no batteries in it luckily. I noticed the bottom of the engine was damp with what appeared to be an oil. Does anyone have any ideas on what is needed to get this old timer going? Thanks.

I got the Bachmann's Big Hauler #90-0100-27 out of the attic for the first time in 20 years. Hoping to surprise the grandson with this running under the Christmas tree. Luckily when I last put it away I took the batteries out of it. But with new batteries installed the engine will not run. The RC control lights up but no power to the engine. All switches are on.
There was a little oil (or it seemed like oil) coming from the motor compartment. The bottom of the case was damp with it.
Any ideas where I can start to make this run again?
Any help will be appreciated.
Thanks