Fantastic looking product, tempted to buy your cups myself, especially seeing as I'm leaving the Suzuki dealer soon to work at a BMW one! (they should have the special tools!
).
One question, you mention here (and on your eBay advert) -
A captive design is preferable for long term reliability as it leaves no chance that it can come loose, vibrate free, or fatigue and fail as has been observed with clip-on caps
Are you referring just to the OEM plastic ones or the metal aftermarket ones too? If both, do you have any evidence of the metal ones failing? If so I'd like to see photos of that (as I'm considering the clip on ones to save time). If not, you ought to clarify your advert.
If this isn't the place to ask, please direct me to where, or create/ask me to create a new thread.
Cheers
Mark D. (a previous customer of yours).