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Noticed black dust in the bilge after our last outing. Am I starting to lose my belt or maybe water pump? I dont see any areas of the belt that are chewed up and it rotates smooth with engine on.

Are any of the pulleys rusty? The research I did always led to people saying the pulleys are out of alignment. Mine were fine but still was getting dusting with a new belt. I had the same problem when I purchased my boat. Both the power steering pump pulley and alternator pulley were very rusty. I replaced the power steering pulley with a new one, however I could not locate a new alternator pulley due to it being a special size. I had an alternator repair shop bead blast the pulley and sand the inner edges smooth then painted the pulley and alternator before reinstalling. While I was in there I removed, cleaned, and repainted the water pump pulley as well. This solved my belt dusting issue 100%.

This is the only pulley showing some rust, but not on the belt contact surface

Could be alignment then. In the video it kinda looks like there is some brown tint on the alternator pulley where the belt rides. There is definitely some fraying on the outer edges of the belt. That's where my dusting was coming from as well. Id pull the belt off and check to make sure all the pulleys are nice and smooth and use a straight edge to check the alignment.

Looks like its the power steering pulley

That just might be the culprit. Judging by the cords on the outer edges and wear of the V grooves the belt is definitely coming in contact with something abrasive. May not be your case, but it's amazing how these repair shops do not dig into the root cause of customer reported problems. Seems like shops nowadays just throw parts at it and hope for the best. My boat came with a laundry list of maintenance/repair documentation from a Cobalt dealer in Seattle since it was new. The last few customer reported problems were belt dust in the bilge and the dealers solution was to replace the belt for the two years before I bought it. Replacing and resurfacing the pulleys was the solution for my dusting. I also replaced the belt at the same time I did the pulleys even though it was only 6 months old. I put the old belt in the tool box for a spare.

Cords on outer edge are normal; this belt is brand new OE VP.

How old are the belts that are on it? If they're pushing 10 years old, it's probably time to replace them anyway. Might as well check the pulleys with a straightedge and feel for any dinged up spots while you're changing them. Lots of good advice above regarding pulleys being rusty or abrasive and chewing on belts too, and how to fix that.

Wire wheeled the pulleys and repainted

After picking up my '08 252 and launching it I had an issue w/belt getting thrown once I got rpm's up. Inspected EVERYTHING looking for pulley alignment issues, idler problems, bad bearings, etc. You can see from pic there was lots of dust around the PS pulley area. After checking fasteners I ended up discovering the top bolt on the PS mounting plate was stripped. It threaded into the aluminum alternator mounting bracket and the threads in the aluminum were stripped. Installed a heli-coil and all is well. Apparently that stripped bolt allowed the PS bracket/pulley assy to flex once rpms were high enough and that resulted in enough misalignment to toss belt.