Thanks for all the input!
I guess I need to look closer at the service manual, thanks Erland. It seems Canon's projected lifetime for those monitored parts is 20,000 A0 sheets, or 200,000 square feet, so I'm barely started!
One head is dying of of old age, almost 700 days and well past 10^12 dots. It's still working, but it's got the tell-tale slight leaking that means the end is nigh. The other nearly new head died of a piece of metal embedded in some media. Not happy about that.
It looks like the 8300 will be a keeper for now, since I already replaced the dead head to keep going on a special order that came in this morning, and I also ordered another head. Had been holding that backup head since December to cover me in case the old head died during the 4 day holiday weekends, since January is my biggest month. The 1 year warranty on heads starts ticking on the invoice date, so I didn't want to delay much longer.
And quite frankly, the logistics of swapping printers is no fun at all.
Yeah I hate to create a landfill bump that big, and Jolene deserves so much better than that. I think I will look into the school donation option in a few months.