I regard the on/off lever as a standard operating procedure - turn on, insert, align the zoom ring, turn off, close the housing, turn on and verify that it's working, turn off, pump out the air.
The 10-18mm zoom ring is quite fiddly - needs to sit just right in order to not rub against the housing which stops it from turning, yet engage the gear teeth; that's an interesting suggestion you have regarding the silicone grease on its surface. The 16-50mm ring has never given me any issues.
I 've been inserting the camera turned ON following a previous suggestion from you, but it does not seem normal than in can be inserted OFF without zoom gear and OFF when using a Zoom gear. Evidently the zoom gear forces the camera to sit in a different place.
Currently my usual procedure is: Put the zoom gear in place, turn the camera ON, put the housing lever in ON position, insert, verify is working, close housing, check again if working (due to fact that when closing knob made ressitance to spinning), turn OFF, Pump out the air, wait (and now having the problem of VPS-100 turning itself OFF), replace the cap.
It is esentially similar but most of the times I do not need to align the zoom gear. Once in its place, the lens passes thru without changing its position.
I see you are having the same problem I had with the 10-18 gear, but not with the 16-50mm.
Which port do you use with the 16-50? . I ask because, even as it makes no sense, I had the problem with the threaded macro short port, not with the 6" dome nor with the standard port.
Try the silicone solution with the 10-18 and tell me if it improved.
regards