3rd Battery Reconditioning

My 2008 Prius threw the triangle of death last week. I watched the banks using the Dr Prius app and noticed bank 2 would sometimes work correctly and then a few minutes later would drop low in volts causing the voltage differential to rise up over 1.5 volts. I've had battery problems twice before and removed the pack myself, reconditioned the cells replacing the bad/low cells with better used ones from Ebay. I discharge to 6.3v at 1.5 amp and charge at 5 amp.

The car has almost 300k miles and I'm thinking the cells are getting past their useful life, but I just don't want to spend the $2k or more to get a new or reconditioned pack. So my plan is to keep reconditioning myself and hopefully get 12-18 months between failures.

One thing I've never understood is how to match cells together into banks. My previous approach was to place the highest mAh battery with the lowest, the second highest with the second lowest, etc. Can anyone help be with the best approach to building the banks, and also when do you determine if a cell is no longer useable? I've been getting rid of any cell below 5000 mAh, but again don't know if that's the best approach.

Any help appreciated.