Minecraft 1.16,3
Forge 34.1.25
Create 1.16.3_v0.3a

I added glue to a piston head, but no matter what I add to that, it does not pull it back. I tried chassis, regular blocks, and slime blocks. As you can see in the screenshots below, it's like the piston leaves the glue behind.

You have to use a sticky mechanical piston. Use a slime ball on the piston head or use the crafting recipe.

Maybe the description of the item should say that. When I look in JEI, the items in this mod are in seemingly random order. No similar items are even close to each other. Without pouring through crafting recipes and descriptions of every single item, it's pretty easy to miss that there are sticky versions and you can't just use the glue that everything else uses.