It's a very common problem, and unless genuine parts are used people have had pattern kits fail again within a few thousand miles...
With the price of the cars you have to weigh up if it's worth the cost of replacement.
the filler plug was manufactured too low on the box, so you cannot put enough oil in, causes the failure of the box, incredibly common issue and a known fault, no guarantee a replacement box wont suffer the same fate.
That's probably down to the gearing and weight difference between the cars more than anything else.
Is the idle of the car smooth?
This is my old Autech Pulsar, you can hear there is a noticeable lope to the idle