I bought a lovely old 35mm Summicron from Red Dot Cameras in London - very friendly and helpful - and ordered a hood and UV filter separately. The hood fitted perfectly, but the filter was not the best of fits, so I dotted a couple of drops of superglue between the hood and filter. Perfect!
Except that two days later, when I went to use the lens, the front element had turned white. I Googled the problem, and found that superglue fumes wreck lens coatings.
Fortunately, we are covered for accidental damage, and our insurers will pay out, but it's a sad story.