My favorite zoom has acquired a problem, the supplied lens hood is falling off loose. I purchased a couple of different cheap lens hoods and really didn't like either one. One did however work, OK. The other vignetted. I thought I had lost the original lens hood, so I found a supplier and ordered a new one. Alas this one was as loose as the first. So, obviously something has changed on the lens, but what? The bayonet looks just fine and there's no scrapes, scratches or whatevers. Has anyone else encountered this problem and were you able to fix it? Thank you in advance for any advice.