As he just said, if your box is going to go there no warning, just CRUNCH/BANG! The diff is crappy, has plastic parts, etc and it can go at any time. Take a look a few pages back at my post which shows what it looks like if it does decide to go
The car had less than 20k on it at the time...
Don't worry about your clutch, they don't usually give issues. For reference my clutch is new - thanks to gearbox exploding as said - and the bite point is a bit higher than half way, which is normal for an ST (and all Fiestas) as they have a hydraulic clutch.

Don't worry about your clutch, they don't usually give issues. For reference my clutch is new - thanks to gearbox exploding as said - and the bite point is a bit higher than half way, which is normal for an ST (and all Fiestas) as they have a hydraulic clutch.