IMO the ONLY seal that won't leak on a Pontiac block is the Viton BOP seal. HOWEVER, there are a few tricks to installing them CORRECTLY. I had our mechanic friend install mine in the Bird, with the motor in the engine bay, both motor mount bolts removed and the engine lifted just enough to remove the pan.

Once that BOP seal was installed, not a drop since! The rope seals on the market are not the same as they were years ago. There is something different about them and they all leak eventually...