6400 toggle wheel problem please help

Hi guys...i am purchasing an EMU from some one abroad...they had mentioned that the only little problem with the unit was that the Toggle Wheel was 'a bit weired'.......is this something that I should avoid all together and no purchase the item? What exaclty does the toggle wheel do...? and is it something that I could possibly fix myslef DIY?
Thanks...any info is appreciated
Thanks...any info is appreciated