SDM Reliability

Hello!

This is my first post to dp, but I have always been a Pentax person, (anyone remember the SV)??

Having stuck with the brand I now have a K20D (thinking K7), but currently may buy a s/h DA* 50-135mm F2.8 ED AL (IF) SDM. Its at a reasonable price, vgc and apparently 2 years old. However looking round the Posts there seems to be several comments re SDM reliability although I get the feeling they more relate to the 16-50mm?

I know the glass aspect of the 50-135 is good, but even s/h it’s a fair chunk of money and I really don’t want to splash out if the SDM is unreliable.
Any views please? Thanks.

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pnt