[zabatron]

I bought a WQ Fiesta XR4 brand new back in 2008.It had the 3rd gear crunch issue from new, most noticeable when shifting down to 3rd gear,and it jumped out of 2nd gear when decelerating a few times as well,also from new.Of course the Ford dealer's response was that it was normal, and "they all do it.
Anyway,these issues got a lot worse,along with the cold shift performance, at@30,000km,when an inspection of the gearbox oil found it to be black, smelly and very much burnt.I replaced the gearbox oil first with the genuine Ford gearbox fluid, then with the same Penrite Pro Gear 75w/90gear oil as recommended on the Penrite Website,but the above issues remained, and the cold shift performance was very ordinary with both of these oils.Note this was around 10 years ago,so both of these gearbox fluids may have been reformulated since then.and may work better today than they did 10 years ago.
But from my own personal experience the best gearbox fluid by far for the Getrag/Ford IB5+ gearbox used in the XR4 is Castrol Syntrans 75w/85 as it cured all the above issues in my XR4,and shifted perfecly both hot or cold until I sold the car at 90000km about 4 years ago.
If it was me,I would change the gearbox fluid before changing out gearboxes.