I have a Zenoah G-26 on the front of my 1/4 scale Sopwith.
It came ready for smoke, with the B&B system, and that's what I installed.

Here's the scenario.
When I run the engine, I get an oily spot in the bottom of the inside of the fuse where the gear is installed. I used to think that I had a leak problem with my smoke oil tank. It's definately not gasoline, I've smelled it repeatedly to verify. It actually has very little smell at all.

Here's what I think is happening. I have a servo that controls the smoke oil valve. That smoke valve is on the firewall, so I use a plastic pushrod to operate the valve. A flying friend was sharp enough to point out to me that he thinks exhaust residue is running from the mounted valve down the pushrod and dripping when it finds the servo. (the servo is indeed covered with the same oil).

What I suspect is that there is backpressure from the engine muffler that is traveling through the smoke oil tap and tubing, and it's getting past the valve and running down the push rod. Then it drips inside the gear compartment.

Assuming this is what's happening, any ideas on how to stop it? It's all the stock setup from B&B, but this is my first smoke system. So any thoughts are appreciated.