I use an F4 camera (lovely but heavy) and an excellent, silky smooth, 55mm Micro-Nikkor lens that has suffered none of the problems I was warned it was prone to. I am only thinking of buying two AF lenses, the 300mm f4 & 16mm full-frame fisheye - everything else is & will be manual. I do hope those lenses prove to be a bit more robust and reliable than the one you are describing.