If your starter is original, I've always believed it is best to replace both. If the solenoid is dead, you can probably replace it but is the starter that far behind? Why remove an old part from the car, swap one piece of it, then put it back on?
I'd personally buy a good rebuilt starter (Bosch) and replace the whole thing. You should be OK without risk of being stranded for many, many years.
Anyone else, please feel free to disagree with me.. that's just my personal opinion. I treat these parts like headlight bulbs - you can replace one but the other is just as old! I can't tell you how many times I've replaced two bulbs a week apart 
Neal
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