[93cobra1928]

There are several good threads on eectuning that talk about setting it to E-10 personally I don't see the need on pump gas because the blend changes a couple of times a year and you never really know.

IMO the exhaust leak even though small will be an issue simply because you have no way of knowing how much oxygen it's letting in the exhaust stream and how much of it is saturating the WB. As it goes through several heat cycles this amount will change. An exhaust leak never gets better on it's own only worse over time.

You said you have the WB tapped into the EGR pin, is it on the ECM itself or are you tapped at the other end? It really needs to be at the ECM so that the signal doesn't degrade from resistance due to wire length.