I have plenty of flush, in fact, I have another 700ml bottle on the way so I can hibernate my 3880 when I'm away. With the 3880, I never put the colour carts in it. My reasoning is that I have never had an issue with any Epson printer at delivery. However, getting rid of yellow is hard work.
My plan is to put a set of carts with Piezography ink in on the basis that it should work. If there is an issue with the carts leaking or not getting a good nozzle check, I'll try another set with flush.
I'm only planning on putting the Epson carts in if I encounter any issues. I started my 3880 this way and it worked very well. I now have a new set of colour carts to use in my other 3880.
I may be crazy but it occurs to me the highest probability is that my first 1430 was the issue.
Cheers,
Jeff