Originally posted by Jonathan Mac Auto focus repairs to SDM lenses are well known to be short-lived. I hear there's a version 2 of the 16-55mm coming out some time soon but the whole DA* range of lenses is well overdue a re-design, more than anything to fix the AF problems.
While some have had no problems with these lenses, many people have. I just avoid them, which is a shame because there are some I'd really like to have.
With the exception of the 60-250, all of the ones initially released 16-50, 50-135, 200 and 300 are fine when converted so the risk isn't that bad. The 16-50 however has not the best optics on the wide end and needed a serious look from Pentax. The 60-250 is probably largely irrelevant due to the 70-210 f4. The 200 probably needs a redo, it's basis is an older film design and it suffers from a bit of ca. The 300 and the 50-135 are excellent optically but they are slower to focus than some would like to see. If the optics could remain unchanged and faster focusing was achieved I'm sure we would all be happy to embrace changes.
However if you look at it like me, those lenses are a fantastic bargain today. Get one with a bad sdm motor and convert it and enjoy it.
My theory on lenses with multiple repairs is that something in the lens or the environment (camera perhaps?) is not getting addressed during repair causing another premature failure.