I've just been through this dilemma. After 10 years out of action, my filler cap was corroded into the tank and I had to completely destroy it to get it out. I initially ordered a brand new replacement filler cap and key barrel from BMW in Germany. It didn't seem like a huge drama apart from the $430.00 AUD that they had quoted. Several weeks passed by when I decided to call them and find out where it was. They told me that they didn't have a filler cap for a 30 year old bike in stock and that they would have to make one.
After several more weeks I called them again and they told me that they would not make another.
Enter Munich Motorcycles in Western Australia! They can get an aftermarket filler cap from Germany. Check it out at;
http://www2.munichmotorcycles.com.au/product_info.php?cPath=2682_1684_1868&products_id=5855Oddly enough, it arrived today and I've fitted it. It's not the same as the original, but it still looks pretty good. The workmanship is as good as anything BMW has produced. I expected that it would be because it is indeed a product from Germany.
The Monza style filler cap is a "Flip Top" cap, similar to what is on my R75/5. It has no key. I'm not sure why BMW made the filler cap lockable. If anyone wanted to milk the tank, all they have to do is cut the fuel line and turn the fuel on.
I'm very pleased with this product. I don't mind that I no longer need a key to fill up the tank.
I'm not certain if BMW still sell the key barrel for the original filler cap, but it's worthwhile asking at your local dealer. If they can get one, you'll need to supply your VIN. Assuming that BMW can supply the barrel, they'll be able to set it up so that your original key will fit it. Apparently they have the information to do that in Germany. It'll also cost about $130.00 AUD........if they can do it.
