I recently changed the fluid in my four speed. Not being able to find the reccomended GL4 90W I used valvoline 75W- 90. The fluid seemed very thin and now I am having trouble getting into third gear both up and down. I realize I may have a syncro issue but this did not exist before the fluid change. I would like to try a different fluid to see if that is the problem. I would be gratefull for any advice on what to use and where to get it. Thanks!