Slicers are a breed of there own. The problem with the 7512 is that it can be 4 different designs and you have no way of knowing if the parts have been mixed and matched. Very common on these. Also aftermarket parts, especially blades and bearings. That said, neither you or I have any idea what you really have. A date of manufacturer would help to get you back to original and the right parts diagram.
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  The problem you described is common. The blade guard is held to height by the hollow core center that the blade shaft rotates around. The shaft/blade is high due to either a snap ring failure, loose shaft retaining nut, Miss-installed bearings, or wrong/miss-installed blade. I have also seen The blade guard hub worn from operating loose over many years, but not common.
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  If you can not find a date of manufacture, you best bet is to find a slicer repair shop. They will know what one you have and if it was put together right.