trouble shifting into certian gears

[Siffl]

i recently acquired a '92 240SX SE manual. i was taking it out for a drive and i noticed that while i was moving at or faster then about 75 MPH i was having trouble shifting into 4th and 5th gear. whenever i would go to put the car into one of those gears the gears would grind like i didn't have the clutch in but still go into the desired gear with no more effort then normal. a little worried i called a transmission place, and described the problem. the mechanic on the phone told me that it sounds like the bearings had gone bad and it would require a lot of work and money to fix, if that happen to be the problem. my questions are as follows. first, does this sound like a good analysis of the problem (granted, without looking at it). second, if it is a acceptable analysis, what are these bearings the man speaks of and where can i find them on the net (to get a rough idea of prices). thanks in advanced

[NISTECH]

Grinding into gear does not indicate a bearing problem. A bearing problem typically comes about in any gear and is a steady humming noise. A grind into a particular gear typically indicates worn syncros.

[Shift_Tommy]

i hear that changing the transmission fluid with some redline usually makes a big difference