Hi @zurn,
This thread may be of interest 
If you continue with a flathead screwdriver it may be worth getting one that’s intended for electricians, because the anodisation can round the corners slightly, and from a hardness perspective is also less likely to scratch the similarly anodised surface of the flange.
Depending on what (if anything) is attached to the flange, it may also be possible to reduce the static friction by rotating the flange slightly side to side while pulling it out.
Indeed. The cast acrylic tubes have reasonably significant diameter variations that make it challenging to use the same seal components and achieve a similar level of seal across the range. Some will inevitably be quite loose and easy to pull off, whereas others end up very tight.
The machined ends in the new locking enclosure design tightens the tolerance to ensure a more consistent seal and amount of movement resistance from the seal compression.