Not sure if there's a test for the turbo seals, but check the oil cap for tell-tale signs of water in the oil
One other option might be the radiator - my Toledo was drinking coolant at a similar rate and it turned out the radiator was corroded to buggery. It was only leaking with high temp & pressure and probably would have lasted another year.... but the water pump impellor fell off and the sudden build up in pressure blew a chunk out of it :-(