I don't think you'll encounter any mud as it's nearly all rock base, there may be puddles if it has been raining. We did La Brigue to Limone and then down the Colle de Tenda . I'm not at all annoyed that they charge to ride it now (they do the same for the Sommellier now) as it pays for the upkeep of the road and allows it to remain open.
My mistake with the distance , it was about 23 miles NOT kms.