Never had one apart.I have put many hrs on one, but if they are like any other trimmer at the end of the shaft where the head is there is no bearing its more like a bearing surface for a big long spring that is your drive shaft. Why spring? To absorb some shock. Some are driect drive with a clutch. It being a sthil there might be a bearing I don't know. I don't think that the 72 is direct drive but I do believe it has a clutch. If when its idleing and the head is not turning there is a clutch. Were you trying to trim really tall thick over grown weeds at a fast pace with it bogging down the whole time, then it did this? If so the drive spring could be twisted and binding inside the tube it rides in. Take it apart. Can't use it now any way. Remove the screws that hold the power head to the shaft pull it apart and the drive shaft should be right there. One way or another it should slide out. Either from the top or the bottom. Then you will know if it has bearings, shaft or spring drive, clutch or clutchless drive or surplus grass, or something tangled around the trimmer head.
