As much as it needs. I use the GM stuff, after I changed my rear end oil last spring I put 1/2 bottle in, its a small bottle. Seemed fine but a few days later it was cracking going in to my turn around garage-its a PITA.
So in went the rest of the bottle, still was making noise, few days later got another little bottle, gave it a another 1/2. Nope, 2 weeks later I still hear some noise after it was hot. So in went the rest of the 2nd bottle. Been fine ever since.