Ta for the info Martin, it worked just fine. I had actually tried that approach when I asked the question, but was struggling because I couldn't extend the leg after refitting the collets. Turns out that the spring was catching on the spring clip and all it needed was a sharp tap whilst pulling the stanchion upwards.
Cheers, Mick.
P.S. Does anyone know of anywhere to have the Marzocchi rear shock refurbished?