Take great care with bearing adjustments. If my 701 is anything to go by, MC carts take no prisoners and chatter can ruin an otherwise good sound. I had no "rock" but there was the tiniest bit of vertical play if the horizontal gimbal was held and firmly rocked up and down. Adjusting this out and adding a tiny drop of fine clock oil cured this completely (and improved arm friction too..) but I'd hesitate in your case as spares will be impossible to obtain for the PL71 (there's tons of Dual bits around and I have a spare "bitser" from Shane - thanks again sir! ).
Tear down these walls; Cut the ties that held me
Crying out at the top of my voice; Tell me now if you can hear me