When I replaced the cord on my soft top I used the cord listed below. I searched all of the internets (yes, all of them) and it appeared to be the best choice. 3 months and so far, so good.
3961T31 (Same as 3961T3)
Chemical-Resistant Polyurethane Cord 5/16" Diameter, Black
In stock at $1.09 per Ft
Polyurethane Cord— The premium choice. It is non-marring and stands up to oils, ozone, salt water, and many chemicals. Cord stretches up to two times its length and has a good "memory" that prevents it from permanently stretching.
Heavysteven, which cord from McMaster Carr did you use? The EPDM Rubber Cord or Polyurethane Cord?