I could not find a parts list for the given model number.
If I "overheated/melted the motor to pump seals and now the motor is seized", is this repairable?
Yes it is repairable.
Does it mean a new motor?
I would replace the motor/pump assembly but if you are mechanically inclined you could replace the seals.
There is a possibility that you burned out the motor so that is why I would go with the motor assembly plus it is much easier.
Is that cost effective?
A new motor assembly will run you about $150.00
In your case it does not sound cost effective because you do not use the unit.