is it just 4th gear or all of it?
 

100 miles into a 180 mile trip i noticed burnt gear oil smell. with kids going crazy i went ahead to my destination. after relizing my manual tranny was EMPTY and that she refused to quietly go to 4th gear. i added 2 qts. and drove it home. now it has the recomended 2.83 qts. she still doesnt like 4th gear much though we have compromised by using engine rpm's to "float" into fourth with only a few clicks of grinding each time. i drive it daily and nothing seems to get worse. what have i done? how do i fix it? any educated ideas would great!