I've had a major leak from the rear RHS of the engine bay. Fairly viscous, pale pink, sticky fluid - about 300ml/half a pint.

Suggestions so far have been a crack in the radiator expansion tank [S Types have this problem] or possibly from the steering or garbox/drive train.

Any thoughts or suggestions?

 

I'd vote for the expansion tank.

My best suggestion would be to get your head in the engine bay and see where it is coming from