BicycleBoy, I'm almost certain mine does have a drain bolt but for now, I'm going to (attempt to) undo the return line at the radiator and drain it out into a measuring jug ~1L at a time, topping up after each litre, for two litres' worth. I know it's slow and inefficient, but it should be one of the easiest to do based on my current equipment. If it's properly seized on then it can wait, but unfortunately, I cannot afford to be stripping threads and stuff when I don't have a replacement bolt (let alone pan) and need the car daily for the next couple of months. I do appreciate what you're saying though, and agree that in theory, it's the simplest method