Seems a common problem, I think I remember 3 or 4 threads about it in the last year or so.
Don't know what eziflow is, so I can't comment on it as a way of connecting copper to steel
As far as replacing the line with copper and brass fittings, I wouldn't have any problem with it, as long as the line is attached to the engine
so that it vibrates in concert with the engine
. Copper line will work harden and crack from vibration.
In the past when I've heard about this, I always wondered why people who have this problem don't just go to braided stainless. Something this small could probably be had for less than Yanmar
wants for their not-so-good steel line. Plus they look cool.
Stainless lines are readily available, from hot rod parts
stores and industrial instrumentation suppliers. A quick online search yielded this superduty 1/4" braided steel line, 18" long with 1/4" NPT male threads for 27.83...
1/4 In T321 SS Annular Corrugated Metal Hose Assembly With T304 SS Single Braid, AF4750