Focus issue on 28-70mm f2.8

Hi,

I just received a used 28-70mm f2.8, which was advertised to be in great working order, but looks, talks and moves like a lemon...

I discovered soon that the autofocus didn't work properly. I tested it on two bodies, D600 and D70, but to no avail. When I examined the lens closer I noticed a significant resistance around the 3 meter indicator, both when turning from infinity and when turning from lower values. And when it passes the 3 meter indicator the lens makes a low sound, like a shift?.

This resistance is particular apparent at 28mm, where I have to turn the focus ring several times when moving from lower values before it passes 3 meter indicator. Moving the focus ring from infinity at 28mm does not require several turns to pass the 3 m indicator, but there is still the resistance and the low sound.

I've googled and found next to nothing, except some chinese texted youtube video of a 28-70mm repair for what seems be a similar fault (the first 10 seconds) . In this forum I've only found one similar thread, but it provided no answer (just the answer for another poster's issue...)

Anyone with an idea of the cause of the resistance and perhaps an indication of the cost of fixing it?

Kind regards

Eyvind