I am having a similar issue with my sony r2r. The supply reel works as expected, but the takeup reel is too slow. Do you have a specific part number for your capacitor?

Looks like this one, but I'm also interested in finding it on Mouser or Digikey

edit: I fixed it (so far) by disassembling the reels and cleaning out the grease. Now it actually plays! I'll still probably look into replacing the motor capacitor eventually, but for anyone else with the same issue, invest in some denatured alcohol and qtips and go to town.