Epson P-800 Clogged Black

[compguy07]

Client brought in a P-800 that had some clogs. They said they did a bunch of cleaning cycles, but still getting bad nozzle checks. I flushed the cleaning pads and cleaned the wiper with Piezo Flush. Did the wetted paper towel with Piezo a few times wiping the print head. Some head cleanings and one deep head cleaning. Nozzle check is perfect, except on the Photo/Matte Black. I started with maybe 30% of the lines showing. Now, maybe 35%. I let sit overnight and did some more nozzle checks and couple more normal head cleanings, got maybe 3-4 more nozzle lines to show on the nozzle check. Would changing back and forth from Matte to Photo a few times single out cleaning that spot w/o wasting the other inks? I'm thinking last resort would be cleaning carts with Piezo. Anyone know, if only one ink is clogged, can you just do a single cleaning cart with Piezo and leave the other inks in or do you have to buy the whole cart set and run Piezo in all? The former would be much cheaper if that would work. I'm also wondering if the client did back to back cleanings too many times and possible damaged the print head in doing so. Any other suggestions?