I don't know if a reply now is worth it, but I can pass on what I have learned about my old 3800. I also started the photo black smear and loss of photo ink when switching between the two. I used the matte black as there was no problem at all, but kept researching a fix. As most forums for the Epson larger format printers point our the majority of problems seem to be print head blockage and smearing and everyone points to the dampers. I found a video on you tube showing how to open the printer and get to the print head assembly -- and then I took it apart (one screw under the motor) and flushed it out. I then reversed the video process and reassembled and tested it -- I did not solve the problem -- but I learned quite a bit. As others have pointed out, you can get dampers on Ebay or through other retailers - I found a number of parts through a company called Aliexpress.com. They sell quite a lot of parts. I choose the damper assembly which is all the dampers, switch and motor in a plastic assembly for 95.00 shipped. I did this because after looking at the switch for matte/photo black it is clear that either the motor or the switch could be bad and not fully shut either ink off entirely. They also sell an entire ink delivery system replacement which is what I believe Epson replaces to fix this problem. I did not see any problem with the ink tank holder or the lines delivering ink to the head assembly. I did flush both blacks for the tank to the head because it was easy to do and accessible. ( https://www.aliexpress.com/item/New-and-original-for-EPSON-PRO-3890-3850-3800-3880-3885-3890-ADAPTER-ASSY-INK-SYSTEM/32809121663). I received it in about two weeks and reopened the printer and easily replaced it, also did some cleaning while in there. I also had a head strike problem, and had to put the platen gap to widest to print - so I found the maintenance manual for the 3800/3880 on line and was able to with two screws and a .09mm piece of plastic fix this as well. when reassembled i have fixed the ink smears and platen gap problems. It was not hard to follow the video to open and close, or the maintenance manual. I now have my printer back working beautifully as before. Good luck
