@dlc60 50C is stone cold for the surface temperature of the motor. They can easily run 60-80C for the surface, without noticeably changing the lifespan (80C keeps the windings below 120C, probably, which is their full industrial-lifetime rating in low-temperature motors, typically). I tend to run a surface temp of around 60C under normal, fast-ish printing. During my print run making face shields, I upped my motor current to 80-90% of spec, so I could run faster. Surface temp was then about 70C. If the motors eventually die, tough luck, but they are designed for this.
I have a personal philosophy about tools: they are meant to be used. i don't abuse them, but I use them in a way that gets work done, and if it wears them out, they are doing what they should.