If you had the longer shaft and couldn't get past the damaged splines, the solution would be to cut off the damaged part. I would use a rotary tool with emery stone. Or replace the output "shaft" if you can get that part by itself.

Also; I made a tool for cleaning up hub spline from an old CV axle. Possibly the same can be made from the end of your old prop shaft (cut off the damaged end and have some nice squared off teeth to use as machine cutting tool).

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)