I also have a problem with my Shop Vac 4Hp 8 gal 9.3A model #338-179370. The motor brushes are sparking. I opened it all up & used some compressed air to blow it all out. But that didn't work. I need to replace the brushes. I went to a store Sears Service Dept. They tell me I have to buy a new Motor. but it cost $53.69 + S&H OF $15. (#338 72201-97) So I just purchased a New Shop Vac for $35. I do know of a electric motor rebuilder Company near my house. If they can put in a new set of brushes, I will use it as a back up vac. Depending on cost.