Turn Signal Lens Issue

I noticed the right rear turn signal lens (the clear plastic cover) has parted ways with my Speedmaster. I've ordered a new one, but I don't see how it had been attached. I tried to remove the right one to see whether it was simple "lefty loosey" turn to remove it, but it won't budge. I don't see any flanges or tabs in the housing of the one that lost its lens that would capture/secure the new lens. How does one remove the clear plastic lens and, more important, how would the new one be secured into the housing? I note there is a cutout on the underside of the housing where I'm tempted to insert a flat blade screwdriver and turn it, but I don't want to break anything. Does the lens just snap in?

 

So, it would appear it either snaps into place or, because it's an LED and therefore supposed to last till the cows come home, it might be glued in and not meant to be removed. Just replace the whole stalk if one of them does take a shit?

I guess I'll find out when the new one arrives.

Thanks for the responses.