Yes, your motor brake is slipping. The main cause of this is improper greasing during a PM. If the grease is not purged after the PM, pressure will build up and usually make its way out through the motor seal into the brake.
This is also a common occurrence with over eager maintenance technicians that can help but pump a few squirts of grease into any zerk that they see.
You may want to remove the J2 seal bolt to see if any grease comes out. If you do this, just make sure you're not in the line of fire, the smell of burnt VigoGrease really likes to linger...
When I release deadman switch the arm of the robot starts to sag, seemingly its only J2 that doesn't lock up right away. Looking into the manual the solutions are either to replace the motor or the relay.
Now I am pretty sure its the motor because if it were the relay it would affect more joints I would think.
Is that accurate? I don't want to go through changing the motor to find out it was the relay in the end, how do I know for sure which one is the problem?
How many degrees it slips?
Robot itself can drop a bit after releasing deadman, 'cos brakes need some time to catch the axis 
It's definitely the motor, brake inside is bad.
I have also seen "rebuilt" motors used to replace. And many were bad out of the box.
They are really good at repairing motor/encoder, but not the brakes.
This isn't the one that was leaking around the seal is it?
I know the pain. We started with 25 or so used GM robots way back when. Problems stacked on problems stacked on problems and wrapped in an enigma. 
