Oil and greased can effect the performance of your reel not just by the kind you use but also the quantity. A new reel will often have excessive grease and oil in it. In the long run this will work against the performance of your reel. Grease will eventually accumulate dirt and get into places it doesn’t belong. The usually norm is you grease your gears and areas that mesh or come in contact with each other. You oil your bearings and worm gear. Sometimes a light grease will be used on the worm gear. This is angler preference (the down side to grease on your worm gear is it’s exposed and can gather dirt and debris faster and easier than oil. The viscosity of the oil comes in to play with your bearings. Some oils are lighter then other. So why would you ever use a heavier oil. Some of your bearings have nothing to do with the casting of your reel. An example would be the bearings that some reels have on their worm gear (the worm gear is another area where heavier oil can be used). There is also a bearing at the end of your crank shaft. This bearing can receive a heavier oil or even grease since it has nothing to do with the rotation of your spool. I use hot sauce oil and grease on most reels. A lighter oil is oust and TG’s yellow formula. I also use ardent Reel Butter. I ask the customer what oil they prefer if any.