I saw a thread somewhere where it shows the usual cause of SDM failure and how to make the repair yourself. It was not all that complicated and had complete instructions, but I have only taken one lens apart....several years ago....I still find teeny tiny ball bearings on the floor every so often...so I won't be trying it.
My50-135 is also going out....again. Pentax really let us down with how they have handled this problem...or actually how they haven't handled it.
Still, the 50-135 has superb IQ...I think I will just use it as a MF lens. The SDM was never much faster than MF anyhow.
Regards!