Hi I have 13 43 at differential and 46 or 48 at spur.
To fix the rotor I simply send it to a company near home which makes rotor and they remagnetize it...already tried, it work pretty well.
If you want try make me know...
Ok so look like I have to use bigger pinion...this is very strange to me I never tought a small gearing could damage anything...
Thanks