Lens Flare filter? You must be using Motion 2. It disappeared in Motion 3. It's now a generator and it blows.
However, it's still there. You just can't see it, nor can you search for it. You have to open the Blue Tech Lower Third template. Look around at the groups. There's the Lens Flare filter. Drag it to your FAVORITES folder and it should always be there until you purge your prefs.
In Aftrer Effects, we have the lovely Knoll Unmult function that builds a beautiful alpha out of the premultiplied information. There is not similar function in Motion. No one has built one, even.
This is my standard sigfile so do not take it personally: "For crying out loud, read the freakin' manual."