I had a problem like this , one side would go in fine but the other side would only go in a little way, in the end i just kept taking it out and trying it over and eventualy it went in.... now i dont now if they are actualy handed but make sue you get them the right way round since one side is longer than the other, i dont think that the splines are differant though. 
hope this helps 
Tilly 
		
	
		
		
		
		
		
	
		
		
	
	
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