Digital BW, The Print

So, my trusty C86 finally got a clogged nozzle. Nozzle check
shows it right away. Did a cleaning, waited overnight, and got
the same pattern.  Just did another cleaning, and just for curiosity,
did a nozzle check. Expected "pattern" from "CMY," but "K"
shows no output.

Question:  I have PK in in K, and it shows about 25% ink remaining.
Should I just try a new PK cartridge?  Or should I try the windex trick
(which I've never attempted before)?

Thanks!

Scott