You might inspect the first 6" or so at the left (headstock) end of the leadscrew. That is the part that gets most of the wear, and if it hasn't been kept clean and lubricated each time it is used, it may show damage. Just compare it with further down the screw, to see if it looks different.
If I'm reading the leads and feeds plate correctly, it can't cut 13 threads per inch. That happens to be half-inch UNC, so it is inconvenient if I'm right.
