GybFlex Line Replacement

[AKSailor]

We have a Wichard GybEasy Boom Brake on our cruising sailboat. During a recent crossing, I foolishly replaced a 1/2-turn shackle with a straight shackle on the GybFlex line turning block. Oops! The line chafed through and now needs replacement. It was always too short, and we had tied on a piece of smaller line to make it work: the original line is only 52-ft long. So, we'd like to replace the "official" line with something for which we can purchase as much as we wish. Are there opinions on the line that we can use? Simple 3-strand? Climbing line, since the device looks for all the world like a climber's figure 8?