Could you explain what was done when the arm was serviced. Was it rewired ?
A good test is to balance the arm/cartridge to zero, and set the antiskate to 0, so the arm is floating, and then you can see straight away if the arm has a tendency to swing one way or the other.
I know from being an SME distributor some years ago that often re-wiring had not been dressed correctly where the wire goes from tube to vertical column resulting in excessive pull on the arm one way or the other.

