Had to dismantle camera due to intermittant video. Have not had time to do any troubleshooting but I did discover why the manual varifocal does not work properly. There are two rotating lenses – one for in/out and one for focus. The external adjustment rings each have a magnetic plug that link magnetically with internal magnets glued to arms that connects to each rotating lense. The glue that holds these magnets in place evidently is weak and allows the magnets to literally jump from one adjustment arm to the other so that trying to set the focus is impossible. The fix is to simply re-attach the magnet to the aluminum lens adjustment arm (using a better adhesive). I still have to figure out the short in the camera and then hope I have the skill to put it all back together. I have two other EC550VF and at least one of them has the same issue with the VF.
I am sorry that you are having trouble. Yes, we found that model to have some problems like you are describing after they are in service in the heat for a while. We have since replaced that model camera with this one: