If the power supply runs hotter than originally, there might be a problem with the coils or the driver. If that was always the case, I would suspect the spring. Springs can deteriorate over life, but the exact mechanics of failure involved are a bit mysterious even to experts in part reliability. I had a longer correspondence on this topic with someone from RAC and we decided that more data is needed.
On the other side, coil insulation becomes worse at well. When this happens (shorting one ore another winding) the coil runs hotter AND a higher current is necessary to produce the same force, making it run even more hot and accellerating the insulation failure.