Mine cracked also when I re-assembled it after its first cleaning (9 months down the road). I bought a new sleeve and it cracked also. I talked to the manufacturer about it at MACNA. The grommet/nut that screws down onto the sleeve can be the problem. Since it was still under warranty, he said he would ship me new parts.
DON'T go and buy a new sleeve! They are expensive.
Since it is still under warranty, if you bought it at your LFS, take the whole thing back to them and get a new one in-the-box. They can GIVE you a new one and return the bad one to the manufacturer.
If you bought it somewhere else, return it to them, or call the manufacturer and explain that you want a new sleeve and the grommet/nut. The rep at MACNA was very good about helping me get it fixed.