Canon EF-70-300mm F4.-5.6 focus issue

I'm having a focus issue with my Canon 70-300 (non-L lens). When I mount the lens, I have to flip the AF/MF switch on and off a few times and manually turn the focus ring a few times to get it to focus. Once it starts focusing, I have no issues using it at all until I turn off the camera. I tested it on 3 different bodies (7D, 5Dc, Rebel) and it does the same thing on 3. It just started doing this out of the blue a couple of weeks ago. It wasn't dropped, didn't get wet, the contacts on the mount look fine. It's been mounted on the 7D mostly over the last month since I got the 5Dc.

Any ideas???

The usual, clean lens and body contacts. You may want to try sliding the AF/MF switch back and forth about a hundred times. Perhaps it has a bit of corrosion on the contacts. Of course, if the switch is failing, that may just break it.