Back when 07 series came out I read that 07 parts are compatible with 06 equipment, but have no surety that whoever wrote it knows what they are talking about. We looked at the 407 parts in the store and the impeller, impeller shaft and o ring are identical to ones i took off my 406 a couple of years back, can't be sure about the cover. It looks like it would fit, but does it fit well enough to avoid rattle etc? Reading the blurb on fluvals website it doesnt specifically say 07 parts are compatible with anything other than 07 equipment. I wouldnt even be questioning it but for what ive previously read, and my store doesn't have a kit for 406 in stock.
The store is going to check some more for me and ive contacted fluval as well. If i get a response one way or another ill answer my own thread.
I'll probability get a 406 kit online to be safe. I just prefer to shop in store where i can as long as it doesn't get too pricey when compared to online prices.