Did you go through all the tests? 1 mA isn't going to drop your battery
I have the exact same situation. No matter what I do for storing the battery they die over winter storage.
Gel cell batteries are known for not taking a charge from a normal charger once they drop below a specific limit. I have had several that I took back to the retailer and then they told me the story. Gel Cells require a very large current curge to "wake them up" once they drop below the cutoff, IE 400 amps for an automotive size. I have a 200 amp charger that still wouldn't do anything. This retailer told me that they usually hit the returned gel cells with the proper charge and then use them for their own vehicles and they last for years with proper maintaining.
Get a proven replacement and do not allow it to become discharged. It will work well for a long time if you use a maintenance (trickle) charger.
Thanks for the tips guys, it has to be the GiPro, there is nothing else connected unless you count the on board clock. Wonder if anyone has ever installed a battery cut off switch like they put on drag cars. That would be interesting. You can totally isolate the battery from any current draw with the flip of a switch. But where to mount it?