No responses. I'll chime in late.  It is a TEFC motor that relies on air blown from the fan on the end across those fins to remove the heat from the motor. The rust will impair that heat transfer both by obstructing the channels between fins and by providing a layer of thermal insulation on the fins.   There may be a variety of other concerns... at what point does the stator allow water through into the winding. Is the mechanical structural integrity compromised.  Do you have a good frame safety ground connection. And probably more.

ep,

This has got to be someone putting the rest of us on.  But, I did have a customer with a motor that looked very much like this.  It sat under a leaky pipe while doing it's job.  The pipe?  Filled with acid....