I have a 1.3 Multijet and recently the gearbox has felt a bit notchy going from gear to gear.

Let's think of this scenario...

Going from 3rd to 4th I pull the stick back and it moves slightly, resists, goes into neutral, I keep pulling, resists then goes into 4th.

So:

3rd-sticks-neutral-sticks again-4th.

The gear changes aren't as smooth as they used to be, but the clutch/brake fluid is due so perhaps the clutch isn't releasing as fully as it should?

Well this is a helpful forum isn't it...