You could tell the sticky pieces by the teethmarks from pulling them apart :D

By that standard, nearly all of my pieces must have been sticky.

(And yes, I did grow up in the '80s).

Have you tried these:

  https://shop.lego.com/en-AU/Brick-Separator-630

They work very, very well.

The other thing about Lego is that it's a bit trickier to clone than you'd think. Most of the other 'compatible with other major systems' brands don't come apart as well as Lego does.

It seems part of the trick of Lego is to make things that are appropriately easy to take apart, as well as put together.

I used this one:

https://www.amazon.com/Lego-Gray-Brick-Separator-LEGO/dp/B00...

I wonder about the design change, with this plus-like protrusion at the top. Is it to enforce correct direction of operation when using the separator?

It is to push out cross axles that are part of Lego Technics.

See for example set 10074-1.

I guess that "plus-like protrusion" is designed to fit "tubes" on the high bricks, primary use being removing low bricks from high bricks. I guess one could use two separators side-by-side to firmly hold 4x2 brick, IIRC 2x2 had one "tube" and 4x2 had two "tubes".