The BOP Viton seal IS excellent. However, we HAVE seen some issues when used in a factory block. The seal "groove" machined in the block is not "close tolerance" as they knew it would house a "rope" seal. The rope is self-fitting (for lack of a better description). Due to this, we recommend the GraphTite seal for "stock" blocks. When using an IA-II block and an aftermarket crankshaft, the BOP is the only logical choice.
