The two that were in parallel are fine and in about the same condition. I bet you'll be able to get at least another summer out of running them in a two-6V-in-series configuration.
Take the third dead/dry battery out and save it for a core to exchange when it comes time for new batteries.
I would like to know on what planet was the opinion split "50/50" on whether your 3-battery configuration was ok or not. Right here pretty much 100% of us are scratching our heads asking, "WHY?"
If you received a 50/50 response, where are the people that said it was okay? They should be here arguing with the rest of 'em. The laws of physics have not changed in 3 years.
