The reason I suggested the insert:
Installing the insert will oversize the current hole past where there is already material removed for the current threads. This will allow you to tap fresh material for the insert as opposed to tapping already tapped material, which will have overlapping threads some thinner than they should be, and winding up with a threaded hole with reduced strength in the threads. Similar to what has happened when running the die over the bolt you have in there. Once the insert is installed properly the threaded hole will typically be stronger than a hole just tapped into the raw material.
Not too sure why Aprilia would have used the super fine thread pitch on their stock hardware. Possibly increased strength due to more threads for a given material thickness
Main reason I suggested the 1.75 pitch is the availability of hardware.
There is a shop in Wakefield MA
Metric Screw & Tool - all metric supplier that is a go to place for this type of thing as well.