No, SP10 Mk3 is not coreless. It's a massive 24-pole motor. I never heard any "problem" with it, but it definitely sounds more coherent, musical, or smooth (pick your adjective) after having undergone the Krebs mod, which is directed at the tendency of the rotor/stator structure to rotate counter to the direction of the application of torque (Newton's 3rd Law), which in turn causes the servo to make more frequent minute speed corrections than is necessary and maybe that introduces a tiny bit of roughness or edginess to the sound that is effectively ameliorated by whatever Richard has invented. (It's a state secret.) The Krebs Mk3 is by far the best of the iron pole motors I have heard in this system and probably edges out the others as well, if I were ever to do a really intense comparison. JP Jones has a further upgrade for the electronics of the MK3 that I plan to have him do on mine. (Fidelis Analog, on the internet)
Your TT101 may need to be properly calibrated. JP, who also fixed my TT101, raising it up from doorstop to turntable, says that calibrating the TT101 is a bit tricky. I think it's fair to say that he would say most vintage direct-drives still in use are not working as well as they could, because of lack of proper calibration of the drive electronics. Just a thought.
Your TT101 may need to be properly calibrated. JP, who also fixed my TT101, raising it up from doorstop to turntable, says that calibrating the TT101 is a bit tricky. I think it's fair to say that he would say most vintage direct-drives still in use are not working as well as they could, because of lack of proper calibration of the drive electronics. Just a thought.