I thought it was usual practice to change the gear oil after breaking in a new set of gears. I have used different brands of oil that claimed to have the additive in it, only once did I have a problem with chatter and I added a half bottle of the GM stuff to it to bring it around. I do not know if I would go in blind with more additive than what is needed. I'd suggest new gear oil with your choice of additive already mixed in or the regular stuff and add some.
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I built it one piece at a time and it cost me more than a dime. 
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