Welcome to the BMP Club
I have found that the small plastic spacers that come with the filter get very squashed and out of shape once you remove the filter. Last time I removed the filter I actually lost one of the spacers, although now I have managed to source a suitable relpacement - most hardware/D.I.Y stores sell plastic tubing similar in width to the Original spacers provided, I bought 1 metre of tubing as spare and cut it down to size - just a little tip incase you ever have to remove it or lose a spacer.
LB.