Fixing an MX8, black gunk inside

[hlarsen]

I recently switched out a directional module in the existing MX8 (moved, new pool) to fix it running in circles; it's working well now. While I had it open I noticed some black gunk across some of the surfaces like inside the top, the plastic housing for the directional modules, and a few other places. Some of it rubbed off, most of it didn't budge when I hit it with the pressure washer.

Anyone know what this stuff is or whether I should be worried about it?

 

[needsajet]

No I don't know. Can only think of very well rooted black algae, but that's a stab in the dark.

I would try a bucket of strong chlorine solution and see if anything changes. Brush the spots first, then try a bucket full of 9 parts water 1 part 10% bleach. Leave it in for 15 minutes, then take it out and rinse it. Try it back in the cleaner for a couple hours and see what happens. Should at least answer whether or not the spots are alive.