I have 4 servos in my parts bin and never replaced a one. Use the one off your parts car. Next week I will turn 331,000 miles on the Red of which 220,000 were put on by me.
I understand you wanting to save spare parts when you can but the cruise servo may be the most plentiful part you can get for a Reatta. Your time would be better spent picking up a few spares at a junk yard and testing them on the car before storing them so you know you have good ones.