3-speed manual leaking fluid

Block the tires, put it in neutral, crawl under the car and push the yoke up and down to see how much play is in the bushing. It shouldn't move much. If it does, replace the bushing when you have the driveshaft out. Check the yoke for wear also. You don't want to reuse one with any grooves worn into it. I use 85-140w with a GL-5 minimum rating in everything I have that needs that type of gear oil. The GL-5 rating will work in a sure grip rear end also. I wouldn't use ATF or engine oil.....they won't handle the loads.