It's definitely worth flushing it through - although a sealed system, the pipe is quite 'large bore' and the sheer velocity of the fluid within will mix the fluid from the Master and Slave over time.
I had my Master fail 1 day after fitting a new clutch - but I was incredibly unlucky and out of the 50 or more we've done at the garage, I was the only one to have it so suddenly afterwards.
Typical!
