MTH Mohawk, erratic smoke mechanism, Cure?

I have the MTH Mohawk, with Protosound 2. - The engine runs fine, bells and whistle work fine, but the smoke feature seems to malfunction from
time to time (no smoke at all) for no apparent reason. For example, it worked fine when initially set up last month, but then stopped altogether, despite my adding smoke fluid. Thinking I had added too much, I turned the engine upside down and drained the liquid. - Still no smoke.
Today, I cleaned all the surfaces around the front wheels and driving wheels, and now the smoke feature works well again. - In view of this, I'm assuming that there was some sort of oil or fluid or crud on some of the elements that contact the rails, interrupting the circuit that powers the smoke unit. - Can anyone provide more specific instructions as to what's causing the problem, and, if it's a matter of cleaning, which parts should be cleaned to minimize the problem. (I thought I had cleaned all the contacts initially, but apparently missed something.) Specifically, where is the circuit, and the electrical contacts, that power the smoke unit. (I'm also noticing that the front headlight doesn't stay on, and blinks on and off erratically, although the rear light and red "furnace light" seem to stay on.)
Incidentally, I understand that this mechanism (the smoke unit synchronized with the sound) was what Lionel was using without MTH's authorization, which led to a patent suit in which MTH recovered over $30 million from Lionel.
Thanks for any information or suggestions for maintenance of the unit.
Jim Cate
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