Getrag 420g is much more durable and reliable then zf. Plus it gives you a much greater clutch selection.
The stories you heard could be of individual people and may not apply to you in any way. If a couple of guys had a problem it doesnt mean that the trans is bad.
Now,about those who swap a getrag 6mt fot a 5mt zf are those who want to save weight in competitive racing. I personally now of a guy who did just that.he swapped his getrag6mt for a zf5mt in order to save weight because in the type of racing he does he never needed to go into 6th gear
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