Green Acetone
My secret cleaner is BioSolv
http://www.greenacetone.com/
You can buy it at West Marine for $18.99 / qt
At full strength it will clean ink from any surface, but will attack plastics. Cut 50% (with water) it still easily wipes away ink, but doesn't seem to attack the plastics/vinyls nearly as much.
Tested on a gloss banner printed w/ECO-SOL MAX ink, a cloth soaked with full strength BioSolv easily cleared the ink, but damaged the gloss finish--leaving it dull. Testing with the 50% water/ 50% biosolv solution I found that the ink still came off without damaging too much of the banner's gloss finish.
I see the insides (and outsides) of 5-10 different printers each week, and this stuff hasn't failed me yet. I use a 40/60 (40% biosolv) solution for the outsides-- I vary the strength as I need it.
...as always, your mileage will vary...
~E