Sony PS-X7 direct drive, slipping at 33 RPM

After a recent move, I set up my vinage bedroom system and fired up a Pavoratti LP on the PS-X7 (circa late '70s). After about 4 songs I was immediately surprised to hear the platter start to drag. It followed a slight pattern; drag a noticable step down in pitch, then back to nomral, step down, then back to normal. You could see the strobe lose its steadiness. I immediately switched it to 45 RPM's and it held rock solid. Then switched it back to 33 RPM's only to have it once again slip. I powered down the unit and fired it back up, then let the platter spin for about a half hour. I then put on another LP and it ran fine. The Pavoratti LP was clean and had only been played about twice.

Am I in for trouble in trying to service this table? It's built like a tank.

Footnote: the house has 200 amp service, and the room (and power lines) were renovated and upgraded in the late 90's.

I look forward to your remarks.
Best Regards,