[Marshall V. Daut]

The 600w we are obliged to buy today is not the same stuff Ford used 100 years ago. It may stink the same, but its lubrication qualities are not up to Ford's standards, which is why we need to thicken it up with STP or some agent that will improve the clinging and coating attributes to make shifting easier with less grinding. Because the original 600w was so thick, Ford garages had a special pump to introduce it into steering boxes, transmissions and rear ends. It was too thick to pour. That's why for a couple years, steering boxes had a Zerk fitting in the filler hole. That was NOT for chassis grease! The REAL 600w was pumped through this fitting because it couldn't be poured in. With today's so-called 600w, it can be poured into the steering box like syrup. Try mixing in some STP oil treatment and you will definitely see improvement in shifting ease with less grinding.
Marshall