I've just started restoring a 1941 3/4 ton pickup with 4 speed transmission. The truck had been sitting for many years. When I got it home the transmission was low on oil, so I filled it with 90 weight gear oil. I've only driven it up and down the street in front of the house a couple times, but the transmission doesn't seem to synchronize very well. It wants to grind from one gear to the next. I'm looking for advice on how to properly bring this old tranny back to tip top condition. Also, there appears to be a grease zerc at the top rear of the tranny. What's that for?