I've successfully fixed similar with 'normal' solder, and a normal soldering iron.
It's nothing special, it's not going to take any more current than a regular solder wire on motor or speedo or battery etc.
They (X11, X12s) do melt though, and it's usually gearing... mine certainly was, well, it might have been running it for 10 minutes on gearing suitable for 6 or 7 minutes...
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