Thanks Walker, I've got 8 of those parts coming my way. Figured if I was going to do this I'd just replace all four on the left and maybe the four on the right as well.
Also maybe it changed over time but there may be an error in The Piezo Manual for the 7800
"Hold down the Left Arrow, Down Arrow, and Up Arrow buttons simultaneously as you turn on the printer. This activates the Service Menu."
On mine you hold down the right arrow, bottom arrow, and center button and then turn on to access the Service Menu.