This is the cap and the former owner just put this in no more then 1 year ago..

I cant figure out how to take this darn thing off..Why not a original metal one?

 

I got the same one, three of them on three separate s10 chassis actually lol... they can sometime be a pain. But pushing down and turning counter clockwise is the way to go...

Left field, but making sure there is no pressure in the system right?

edit: should say down and counter clockwise about 1/4 to 1/2 turn. Then should be able to pull up.

sometimes snug, so wiggle and pull.

 

Looks more like a Sprite to me. Much less effective.