Look at what this Pentaxian, who has both the K20D and K-7 bodies, reports about the SDM *body* problem that he faces!
http://www.pentaxforums.com/forums/pentax-dslr-discussion/101639-very-strange-supersonic-drive-motor-problem-anyone-experience.html
Really strange! It seems that the SDM is actually very buggy and totally unreliable, not only for the lenses that are so easy to die, but also it will become usable or unusable with SDM lenses on different bodies! Very terrible after all! :-( >_<
Read Also:-
The SDM Petition Online