Marea gearbox problem

I wonder if anyone here can help me - my V reg Marea 2.0 155 has started whining at around 50 to 70 mph. I (and my garage) thought it
was the wheel bearings, but on checking they found it was bearings in the gearbox causing the problem.
I'm just wondering what the best course of action is now. I've got the chance of a replacement gearbox that's done 60,000 miles (I've done 40,000) but I'm not sure if that's going to be any better given the miles it's done. Failing that, is it worth having the gearbox serviced or should I just bite the bullet and replace it?
Any advice much appreciated, thanks, Mike
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