I think that is rust washing off the springs. Once it begins it's there for good. I have one doing that. My plan is to extend the slide, drill a 1/8" hole in the bottom side of the tube, spray waterproof "Blue Grease" from an aerosol into the tube-hopefully coating the spring. BTW, that topper needs an assist to rewind if we are parked for a month or so. I think that is the result of rusty springs also.
2000 Winnebago Ultimate Freedom USQ40JD
, ISC 8.3 Cummins 350, Spartan MM Chassis. USA 1SG, retired;PPA,Good Sam Life member."We the people are the rightful masters of both the Congress and the Courts - not to overthrow the Constitution but to overthrow men who pervert theConstitution. "Abraham Lincoln"