Originally posted by SpecialK I had a the original 50-200 and 55-300. The 55-300 had a bit better IQ. Eventually I sold both, but now have a Fry's open-box 50-200 WR which seems better than the original. When weeding out my lenses, I kept it over the Tamron 70-200 (size and weight considerations). I'd keep the 55-300 and use a $5-dollar camera condom, or a towel as mentioned.
Further to my previous post, I used to have the original 50-200 also, which I bought when it first came out. My current one, which I bought secondhand just recently, only a year old, is significantly better, so I share your experience on this. Also my current DAL55-300, although not that great, is a lot better than my original metal-mount 55-300, which was unusable, despite being declared 'within spec' by the Pentax service wizards in Japan.
I've had a lot of bad luck with zooms, mainly decentering, which is why I use old secondhand primes a lot of the time, despite the inconvenience.