Let me summarize:
1) Piezoflush worked fine: 3 power clean cycles flushed the line.
2) Installed the first GO cart and performed one power clean. There was residual GO in the line so I just started printing on a blank 11x17 matte sheet. After about a dozen prints, the GO was mostly flushed, so I started printing on some test prints. After about a half-dozen test prints, the GO cart first started to show banding, then stopped printing.
3) I re-primed the GO cart and it printed a few pages, then stopped printing.
4) The replacement GO cart worked for only 2 pages, the stopped working.
5) As a test (that I know regret, see above), I put the flush cart in and tried one print. Nothing printed.
6) I re-primed the replacement GO cart and nothing printed; in addition, Piezoflush contaminated the GO.