Correct Wurlitzer Tone Arm position

I have a Wurlitzer 412 with a P12 tone arm. It has been modified slightly with a modern Astatic cartridge. The problem is that it seems to be wearing the 78s out on the last 1/4 inch of the groves. Is it possible that the tone arm is off center? Where should the tone arm fall (start) on the record? At center, in front of center, or behind center? Just wondering if the angle is off by the time it reaches the end, causing the needle to twist in the groves and wearing them out? Or could I just be using the wrong needles? I am using 3mil and occasionally 2 mil needles.

Thanks -Tony
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I am also having a problem with the needle not always exiting the record at the end of the grove, causing it to skip repeatedly on the end, until I manually trip the record play. Also causing wear

-Tony