Interesting turn on this thread.
I can't really fathom these problems that you good folks are reporting. I have a garage full of HRC Montesas, and the build quaitiy is what you would expect from a parent company that sells several thousand Accords a day. My 4RT has literally thousands of hours on it, and has never once suffered from these maladies. The 2 315Rs in my scuderia never have either. My old warhorse 314R had a whomped top-end, but that was PO induced and had nothing to do with OE quality.
Don't get me wrong, I'm not saying your problems with your Montesas are BS, I'm just wondering what exactly led to these maladies. I was a Registered Honda Technician here in the U.S. for a number of years in a previous life, and one thing I did learn over those years is that for every failure there is a path to the outcome. Some were quality failures sure (very few), most were caused post-sale. Not saying yours were. In my tenure, I investigated and repaired various and sundry failures on everything from Z50s to GL1800s and belive me the quality failures were very few. I'll be the first to admit that Honda has, will, and continue to step on it's own d*ck now and again, but that is a rare occurance and is usually rectified fairly quickly.
Read into this post what you will. I'll be the first to admit that I'm an HRC/Honda/Montesa fanatic, so my outlook is pretty biased. I am however, an HRC/Honda/Montesa fanatic for a very good reason.
Enjoy your bikes. Viva Montesa!