Opel Vivaro Gear damage

Hello Community, I have a Opel Vivaro Combi L1H1 built in 2008 2.5 CDTI, which now has a transmission damage. It has only about 80,000 km on the clock and was moved 90% on the highway in a comfortable driving mode with approx. 100 km/h in the 6th gear! Since I have read the articles here already some time, I thought, hopefully will hold mine! He is really very gentle driving and has also got all inspections etc. just everything you can do so that you can long dr I can’t believe it!! After 80,000 km the beard is gone. Now it gets a brand new gearbox. So far so good. But now my question to the Opel Vivaro specialists here in the forum: Where exactly is the weak point with this gearbox? Is the 6th gear at all usable or should you stay in the 5th gear? Or is the 5th gear affected as well? Are there ways to modify this gearbox accordingly, I also noticed that in my opinion the gearbox gives a wretched rattle of itself at low speeds. Here you get to say that it would be the gearbox synchronization and that it would be normal. My God, we live in 2012! Can’t you build a clever gearbox? It’s not that much in a gearbox. Rather a simple set-up. And then such noises? Now one last question: My gearbox is now about 3.5 years old. The new just so much newer. Was there a gearbox modification at Opel or Renault or was the gearbox improved by the construction that now comes in or is it again the same stand, so you would have to think that in about 80,000 km the next one is due? Many questions… I hope to get some answers here from people who might have been able to look behind the scenes to find out. How things really are! I am already happy about your answers and wish every Opel Vivaro (or equivalent…) driver a good and hopefully damage-free ride! Best regards