Okay, so what I've got this time around is an "Oil Filler Cap" that rotates 90 degrees to lock, locate and seal itself onto the "Rocker Cover" (not sure if you call them that in the U.S. but it's a cylinder head cover!). The Oil Filler Cap has two opposing grooves cut into the external face of it's centre sleeve which line up with two pins that petrude from the inside circumference of the spout on the Rocker Cover.
Essentially, as with some vehicles in real life, what needs to happen is that to fit the Oil Filler Cap you would line the grooves up with the pins and then apply downward pressure as you turn the cap 90 degrees. The inside face of the Oil Filler Cap has a seal around it. (The cap is a dumb solid so the seal is just coloured)
So, can I mate this so that I can get the cap to be removable and also follow the grooves when putting it in place?
I'm thinking that the first mate would be concentric but then I'm at a blank as far as a non-contact mate (that allows removal) but a mate that follows the grooves when located in place?
The two parts are attached.