Tonight while performing filter maintenance I removed the impeller to clean it and a black rubber stopper fell off. Luckily I found it and put it back on the impeller. I reinstalled everything and turned the filter back on but it was making a funny sound. I took everything apart again but the black stopper was missing. I managed to get the impeller installed and working without the stopper and ordered a replacement already, but I am worried that without the stopper I could damage my aquatop cf-300 canister. Does anybody know if I can screw up the filter or what I should do about the missing part?