Got the solution for you. I had a Targa for several years. The plastic cone gets stuck in the aluminum base.
Go to the hardware store and get some liquid graphite that is used to free up old locks and keyways. Put a line of the graphite around the seam on the base (where it meets the aluminum). Let it soak in/down. Won't penetrate the plastic or the aluminum, but will soak down.
Repeat the process 3 or 4 times. You'll probably need to let it sit at least 15-20 minutes between applications. It will finally do the job.
After you get it out, clean all surfaces and apply a thin coat (maybe using a cloth) to both surfaces. Problem will then be solved. After I did this on all four of my seats (and the multiple surfaces), I NEVER had a stuck seat again.
Best of luck.
Tex