I have a 87 and 89 Sentras. Both have manual transmissions and both have over 165,000 miles on them. The shift from 1st to 2nd gear is a bit notchy. I'm hoping to improve this problem with synthetic gear oil. Anyone know what weight I should use? Also, I looked in the Haynes manual and I couldn't find instructions on how to drain the old stuff and where to add the new stuff.