I have a few of these caps on the shelf. I bought them when my son had his M type and I had a D type. They're original Enots caps and will clip into an oil filler with a diameter of around 1 5/8". I'm 99% sure they fit an M type. See photos below which may help. I'd like £25 each for them including P&P. Email me directly at bobholmes251@hotmail.com if you'd like one. Thanks, Bob.