The splined item that is bolted down with the three bolts is actually part of the complete wiper transmission. This would be the complete item under the wiper cowl. Here is an illustration that shows the complete unit.
If there are still splines on the wiper transmission, but the arm is stripped out, you will likely be ok with just replacing the arm. If the splines are ruined on the transmission it will get much harder than simply installing the new arm. You will need to replace the complete wiper transmission. This would require the disassembly of the wiper cowl, and also the wiper motor from the transmission. Feel free to contact me with any questions! Good luck!
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