What is this oily substance coating everything?

[silvercreek]

I opened my bow thruster compartment for its annual inspection and was shocked to find this metallic oily/greasy yet almost powdery coating covering every square inch. It’s almost like an aerosol bomb went off in here. It has a minty smell to it. Blackish green in color. There are no traces of liquid, or actual oil, anywhere to be seen. Photos attached if that helps.

What could it be?

[senormechanico]

If it is powered by a DC motor it's probably motor brushes wear.

[JPA Cate]

^^^ Yes, it is the graphite in some (but not all) brushes that make it feel "oily." Copper is more common these days, but maybe the graphite is better in an under water application.

[silvercreek]

Thanks both, this makes sense.

Is it a sign of a problem, or is it normal/expected operation?

[George_SD]

Not a sign of a problem, Brushes are often replaceable on many electric motors. You will need to check with the manufacturer. For example many older brush-ed drills and other hand-held devices came with a spare set of brushes, these days few include spares.