I got that on my 285 when it's only seen the ice. I had an issue that caused my bike to run hot. I never melted the piston of damaged the bore. Buy it was hot enough to melt the exhaust flange ori GS, the silicone coupler, and and every shred of packing in my silencer. The exhaust port was cover in that same grey stuff. I figure it's what's left after the fuel/oil super heated. Idk. Maybe Jerry will chime in.