Mikuni BST40 slide guide
New. Notice the ~0.020" (0.51 mm) deep depressions in the bottom corners/concentric to the bore (circled in green), as well as the four circular ~0.023" (.58 mm) depressions.
Contrast this with the two following photos of a slide guide from a KTM 640LC4 with under 20K miles (32,187 km) (claimed). The depressions in the bottom corners/concentric to the bore (normally found in the area bounded by the red circles) as well as the four circular depressions are worn completely away. The plastic is worn completely through adjacent to the bore at 10 and 2 o'clock (when viewed in the installed position). Maximum wear measures 0.085" (2.16 mm), which works out to .0042"/1K miles (.07mm/1K km) (!). Emulsion tube wear ensues rapidly when the slide guide has worn beyond ~0.010" (0.25 mm). This carburetor had drilled slide lift holes, which accelerate the wear pattern.