da16-45 autofocus focus issues

I've had my da16-45 for a while now and for the last 2 years I've had some issues where you half press the shutter button and nothing happens apart from a strange noise for a fraction of a second. Sometimes if you point the lens at an object further away the lens will autofocus.

I thought this was my k20 at first but its doing this on my k5ii as well, although the lens was fine on my k100.

The focus ring moves nice and smoothly.

So is this a problem with the lens, do people think it is fixable and how much am I looking at?

Not sure what the problem is, if there is a problem?
I have exactly the same issues with my 16-45.
I find, on occasion, I have to focus on an area with more contrast then it locks on focus. BTW, mine is the Samsung branded 16-45. I'm in love with the results this lense gives and so forget the occasional focus moods