I recently purchased a set of Palatinate cars and dug out a Marklin 37166 to pull them. But the loco was not working well - jerky, running hot, and kept losing power. I finally took the chassis off and discovered the inside was covered with a slightly sticky liquid. Apparently the previous owner had shipped it to me with smoke fluid in the smoker and it had leaked out in shipment and covered most of the inside. A bunch of Q-tips and isopropyl alcohol removed it all and now it runs normally. If you use smoke fluid don't allow it to get all over the inside of your loco.

I used "sticky" but it was just all over everything and seemed to originate under the smoke unit and then run down under the motor and decoder electronics. Not sure if someone used the wrong fluid but it did not seem to be around places that one would oil. I have heard that smoke fluid is kerosene which in volatility is between fuel oil and gasoline. It did not have an oily smell so maybe someone tried a different product.

sound like someone overoiled it or used some really poor quality smoke oil.

Modern quality smoke oil should not behave like that, and some types are also used as a cleaning fluid.
eg this: Steam & Clean Dampfdestillat and this Steam & Clean Reinigungsdestillat (used by Marklin in their lasted cleaning instruction videos)
the only difference between the products is that the smoke oil/distillate contains some perfume to make it smell better.