I have been looking for a replacement motorhead for my Eheim 2217 with no luck for almost a year. The only motorhead that I can seem to find is one for the 2215. Is it possible to use a 2215 motorhead on a canister for a 2217, or are the canister's different diameters? Should I just forget the entire thing and just purchase another 2217? Thank you for your input.....