My car leaks oil, about a pint a month, but I don't want to fix it 'cause I will be rebuliding the engine anyway, is there a way to slow the leak with some kind of additive? What should I use

 

Where it's leaking from? May be it's not that bad to fix a leak. I do not recommend adding anything to oil - more expensive problems can appear. You can try heavier weight oil though, not sure whether it will help, it helped me on Crown Vic.

 

It's leaking from the front and rear seals....and one of the head gaskets

 

That doesn't sounds very good... I'd switch to 10w30 or even 15w50 on summer. A lot of people will argue on that. Just do not put load on engine when it's not warmed up.