How to fit Zanussi FLS-1183W program timer parts?

Recently the timer knob cover has become loose and wobbly when pulling the knob out and turning the machine on. After a few weeks of treating the knob like it was made of glass, it came off in my hand. The cover knob has split internally. I removed the small centre nut that retains the timer knob inner, the knob inner also has damage to one of the splines, this spline fell off when I removed the timer knob inner. I have the ability to buy some new genuine Zanussi replacement parts - fitting the timer knob inner and the timer knob cover should be very straightforward. I also have the ability to buy a new genuine Zanussi timer cam disc - is it worth changing the timer cam disc at the same time ?? - if so, how do I get the old timer cam disc out ??

Any ideas, suggestions or advice would be greatly appreciated.