Marakanetz,
Perhaps it's more a problem of geometry than maintenance. Remember that with a pivoted arm, as opposed to a linear tracking arm, you only have perfect geometry at two points on the record. All other points are compromises. Perhaps with the "extra-long" LPs, the compromise in geometry is more noticeable than elsewhere on the record.
A shorter way of saying it is that your stylus is turned more clockwise relative to the record's groove the farther the arm pivots toward the record center. That will mess up the stylus' reading of the lateral modulations.
Perhaps it's more a problem of geometry than maintenance. Remember that with a pivoted arm, as opposed to a linear tracking arm, you only have perfect geometry at two points on the record. All other points are compromises. Perhaps with the "extra-long" LPs, the compromise in geometry is more noticeable than elsewhere on the record.
A shorter way of saying it is that your stylus is turned more clockwise relative to the record's groove the farther the arm pivots toward the record center. That will mess up the stylus' reading of the lateral modulations.