I have the 785 levers w/Di2 on one of my bikes for about a year. I don't put it in the car but I have not had any problem with bleeding, air getting in, caliper adjustment. It has been setup and forget it, same with Sram Rival on another bike. Only real difference I know of is Shimano uses mineral oil, Sram uses DOT fluid.

Your 6880 Di2 should be the same as the current Di2, wires are the same controllers junctions etc should be the same. They have upgraded the battery but I am thinking the old one will still work on the newer brifters.

Before I got rid of what you have I would find a competent shop and let them look it over.