It is on 2 of the wheels, both on the same side of the trailer. I have only washed them with soap and water at a coin-op car wash. I bought this 2015 Cougar used in November out of state. It was stored indoors where I bought it until December when i moved it to Florida for the winter so, has still not been home. I have about 10 days on it myself, and it is stored right by the lake at an RV park (no road time on it). There does not appear to be anything on the wheels (like gunk of some sort) I noticed this when I wiped the rims down with 303 spray detailer before leaving at the RV place the other day. Since I am not the original owner, I am not sure what kind of help a dealer could offer. I do have another issue that the boat will likely have to go to a dealer on. Not sure how BCB handles these sort of situations. The boat is less than a year old.