Its not just the cost of the ring and pinion. In order to replace the pinion you would need to completely disassemble the trans the pinion shaft also holds half the gears that would need to be removed. I did it once on a broken trans so I know its possible. Then there is the set up for proper gear spacing. That part I have not had to do. Bottom line is it takes quite a bit of knowledge. Of course you may already know this.
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