Abstract: A mixer seal assembly for a closable vessel having a dynamic mixer shaft seal in a bore in a vessel flange and a static seal for vessel transport formable by insertion of a disconnected lower portion of a fast connect coupling which is fast to install on the mixer shaft into the flange bore above the dynamic seal. The resulting seal assembly can seal the vessel for over-the-road transport. The dynamic seal includes a circular lip which sealingly engages the surface of the mixer shaft. The static seal includes an O-ring disposed in a first annular groove in the coupling portion. A shaft bushing disposed adjacent to the shaft seal in the flange bore minimizes shaft runout in the shaft seal and permits use of relatively rigid and dry running materials such as fluorocarbon polymer in the shaft seal.