Now the question is what to replace it with?
A regular o-ring should do the work if I can find the right size? Or should I order parts from MMC?
My advice would be to send your very graphic photograph with a polite but firm covering letter (recorded delivery) to Mr Steve Morris at the Morgan factory. You could stress that this is a known problem due to defective design and materials and potentially very serious. At the very least they should provide you with a replacement cap of the later type. Good luck!
