cartridge mistracks in final 25 of a record side

Problem solved! It turned out that the tonearm wire was being pulled too tightly at the point where it left the back of the tonearm tube.

This was causing the tonearm to be pulled towards the outside of the record. This effect only would come into play towards the end of a record.

I created a little bit of slack in the tonearm wire and the problem completely went away.

So, it didn't have enough travel?

It had enough travel, but the tonearm wire was causing the arm to be pulled towards the outside of the record, like a strong anti-skate setting.