NickPyner:
Aqualize:
[...][...] It could still be a wiper motor but, if that is the case, it obviously has a large and vital part missing, the reciprocating gear. Fortunately it is not too vital for you, but the bit that connects to the spline would probably be useful. [...]
As I don't have this piece my idea use the bicycle gear, somehow centered and then use the welding machine to permanently attach it.