Well Gee, this is about options isn't it?
I worked for a company who's philosphy is repair it unless the cost of repair exceeds 35% of the repair.
I have worked for a companies who's philosphy was to replace the system no matter what.
Here is my advice:
36 years is a great life for a unit, it performed it's design function beyond it's useful life. This is a GOOD THING!
The question you have to ask, what is next. Yes, you can sink close to $500 for a new motor. You can even find that guy down that street that will repair the motor windings for you for peanuts. If you are doing the repair yourself, than the worst case scenerio is time lost and less than 35% of replacement. If you aren't doing the repair yourself:
The equipment options today are much more efficient. Like I said 36y is a great life, but I guarantee you aren't driving that 36yo car back & forth to work nor do you have a 36yo refrig or washer & dryer that you are subjecting to daily family use.