MFC-7860DW drum life 0% after replacing drum unit

[xtratrestrial]

I have 2 MFC-7860DW laser printers I'm trying to get running for the restaurant I work at. I've replaced the drum units and cartridges for both, and cleaned both of them. One reads 68% drum life regardless if which drum/cartridge I insert, and the other reads 0% regardless of drum/cartridge. I've reset the 0% printer to factory defaults, and still it reads 0%.
Both drum units were laying around in their boxes for a few months before install, but both work on one printer but not the other.

I have all of the documentation for these printers, but haven't found a solution yet.