Cameron, stiction is a known issue with piezo motors. You should take this as a fact.
The 16-85 has a DC motor, by the way - which is more reliable than the micromotor. You would be happy to know that Pentax indeed abandoned the SDM micromotors, as in launching new lenses with other types of motors (including piezo), since 2009.
There can't be any kind of capacitor for the reasons stated:
- no such large capacitor being present in a lens
- piezo motors not needing them (they're quite generic
- if piezo motors would need such a large capacitor, they would work like flashes i.e. the AF motor would move once, then have to wait for a capacitor recharge, then again. We're having continuous AF though so...
- if piezo motors would need such a large capacitor, all SDM (USM, AF-S...) lenses would arrive DoA because there's no way to keep the capacitor filled until delivery. Not just your one 60-250 sample.
Don't believe whatever some incompetent spewed in a Youtube video!
SDM is fine. The first type of SDM micromotor used in the 16-50 and 50-135 wasn't, nor the idea of using micromotors in * lenses - micromotors are entry-level technology. I strongly suspect that current SDM micromotors don't fail more often than Canon's, Nikon's etc.
Ring-type SDM is excellent. Well, if that motor "needs" a large capacitor, it must be filling all the space inside the barrel - effectively not leaving any room for optical glass.
Here's the ring-type SDM next to its micromotor sibling:
http://www.ricoh-imaging.co.jp/japan/products/star_lens/special/sp_dfa50-14/img/a6_img_01.jpg