I am trying to change the rear O2 sensor on a 1997 Nissan Altima, but
can't get the electrical connector to release. I know how it should
work by depressing the tab and sliding the connectors apart as I can
easily do this with the front O2 sensor.

This rear connector is a bit grimy, does anyone have any suggestions
as to how I can help get the connector to release? Tips?

Thanks
Christopher