Was it working before you pulled it apart (even with the oil spill?)

I reckon that was likely the smoker unit leaking smoker oil, or possible the airsoft gun leaking its lube (less likely) - neither is terminal, but is messy.

One thing you have to watch when putting them back together is that no wires are crimped between the two halves, and that the turret plug (that the turret loom plugs into) is secured with its screw -- if allowed to dangle it could possibly short.

Another thing is the aerial joiner: convienient for taking them apart, inconvienient because if its not secured its a bare wire floating inside the rear of the tank -- could possibly short on the small smoker pcb etc.

Just chucking around a few ideas...