Unfortunately, BMW only sells new chrome /5 style gascaps with the lock mechanism. I really like the smaller look of the non locking gascaps. I sourced a very good condition aluminum gas cap and unfortunately, the cork gasket is worn.

Luckily, BMW does sell replacement gaskets. I happened to have one in my parts stash, brand new. What I needed to order was a new retaining pin and washer from BMW.
Removing the old one was difficult. I started by shaving the old pin head down with a dremel. By doing so, i was able to remove the old cork gasket and create a flat surface to align a drill bit to drill out the old pin.

I then took the gas cap to my drill press and tried to center my drill-bit as best I could to drill out the old pin. Unfortunately, the drill bit took on the path of least resistance and did not center perfectly to drill out the old pin. And, the old pin’s metal was either extremely hard, or it got hardened from all the heat of the drill bits.
It was one of those jobs that took an hour longer then I had anticipated.
I eventually got it drilled out. Here it is with the new gasket, pin and washer:

I used some JB weld in the old pin hole to fill the area where my drill bit went awry. I then drove in the new pin by tapping it down with a hammer.
She’s now ready for fuel.