I just received another S1 today and this one was used big time. Lots of Chinese dust all over the PCB boards and fan blades. Should I contact them and have them replace it?
Your choice, of course, but if it works I'd say use it. You'd lose a significant amount of income by being without a unit for the 1 or 2 week turnaround, plus paying for shipping to Bitmain. You'd need to mine for many weeks to recover that, and you'd never catch up to what you could have mined by keeping it.
'chinese dust'? Why would you RMA something because it is dusty? get out the compressed air and clean it yourself in a few minutes. You can use 99% isopropyl (rubbing) alcohol and a microfiber cloth to clean the pcb if the air duster isnt enough