3880 PK Ink blotching

[Rusty]

Found this thread (March 2011) with similar problems with the 3800: http://www.luminous-landscape.com/forum/index.php?topic=51818.0
My 3880 prints just fine with MK ink, Recently went to make a print  with PK and found the black not printing, print manager showed the cartridge as 3/4 full, ran cleanings, even a power cleaning, no black. Pulled the cartridge obviously empty, installed new cartridge and get ugly black blotches along right edge of print (looking straight on output tray).
Local 3rd party repair suggested check platen gap (I run it wide or wider) as well as driver version I have version 6.60 which is currently listed as the driver on Epson's site.
MK ink prints fine after switching back and leaving printer turned off for a few days.
So anyone experienced this?
Are we talking a new head, or a new printer?
Thanks

[pluton]

Here's a more recent thread I started that has plenty of anecdotal remedies and advice.
http://www.luminous-landscape.com/forum/index.php?topic=92273.0
 I concluded that if your printer is fairly new and hasn't come close to the maximum print cycles that Epson defines as the lifetime of the printer, it might be worth fixing. 
My 3800 was five years old so I just replaced it with a new 3880 that makes clunking sound each time the paper advances.
 I expect to get two years of light service out of it.  If I'm lucky, it'll fail during the warranty period.

[Rusty]

Well to follow up on this, short version a new printer is on the horizon.
Did the cleaning as recommended in the video in the threat linked by pluton, thank-you for that.
Let the head rest for half hour or so, did nozzle check with MK was OK
switched to PK, iffy nozzle check but blotches on the paper
Printed a text document, ok but not really dense black on bond paper and you guessed it blotches
switched back to MK same document dense black no blotches, printed immediately after the PK print.
Sigh
Anyway Epson has a rebate on till end of January, likely next one not till August if pattern as I interpret it holds