When I went into mine, I didn't, as I couldnt figure a way to get it off without damaging it!
I've never been sure if the replacement comes with the housing attached or not though. Stu may be best placed to answer/check, if the replacement does not come with the housing, it might make it clear where to jimmy it apart with a screwdriver...
Looking at your filter though, it doesn't look too bad...
Your power issue is 100% the switch, they all do that eventually, especially the cylinders. Switches are pennies, Stu should have one in the shop somewhere