Panasonic G7 and DMW-FL360L Flash Issue

Hi

I have the same body and flash.  I have no experience in shooting flash in manual mode.

I did have what seems to have been a rare problem with my flash but it doesn't quite match your description.

I recommend the following test to see if it is your flash.  This is what I did to isolate my problem and it turned out to be the flash.

1. Use P mode and be sure the flash is set to TTL. 
2. Put the camera on a tripod and make sure your target exposes well by doing some test shots.
3. Put in fresh batteries for the camera and flash
4. Set the G7 to take a picture once every 30 seconds
5. Let it run for about an hour
6. Look across the photos to see if there is any significantly different results.

My flash would occasionally do an extremely over exposed image usually followed by an extremely under exposed image but where the Exif said the flash fired.   I really hadn't realized what was going on.  I had the occasional bad shot but figured I had not waited for a recharge or something.   One day I was doing a lot of test shots in a row and I caught it doing a lot of mis-firings.  Now I realized something was Wrong.  Played around with various things, batteries, seating, etc.   I then came up with the test above and could see that over a hundred or so shots it would happen a number of times.

Found a place to do the repair.  They said that one of the major pieces inside was bad.  It was pretty much cheaper to buy a new one, which I did.   I did the same test right away and no problem with the new unit.     I had  the flash for two years and would say I had pretty lite use of it.

Mark