Proper grease specification requires all of the components of oil selection and more. Other special considerations for grease selection include thickener type and concentration, consistency, dropping point and operating temperature range, worked stability, oxidation stability, wear resistance, etc

When two incompatible greases are mixed, one of two things generally happens: the mixture hardens and will not release any of the oil or the mixture softens and releases all of the oil. In either case, the end result is basically the same; there is effectively no lubrication.

The manuals usually say grease every 50 hours, though some professionals usually do every 25 hours because grease is cheap insurance against pin wear. Also, putting in a little bit of grease in every fitting frequently is better than putting in a ton all at once and then leaving it for ages.