It could be running slow because the drive belt is worn or has stretched and lost tension and is slipping. If the belt is over 5 years old, it is quite possibly bad.

It could also be running slow because it has been a long time since the main spindle bearing has been lubricated with the proper type of oil or grease.

I suggest that you remove the drive belt and spin the turntable by pushing it clockwise gently but firmly with your hand. If the main bearing is OK, it will rotate at least 5 to 10 revolutions before coming to rest when it is pushed (with the belt removed).

If it comes to a stop quickly, and does not rotate freely for many turns, it needs new lubricant in the spindle bearing (or the bearing may be worn out).

If the turntable seems to rotate freely, then get a new belt. LP GEAR has one for $18.