Take off the shifter. Drive the little pin out that holds the shifter block to the shift rod. Unbolt the tailhousing and pull it off. WHen the shifter block comes off the rod make sure you don't lose the ball and spring under it.
After that take the top cover off by lifting up an inch and then shifting the cover to the pass side about 1" then lift straight up.
As long as you don't poke around inside you can put it backtogether.
If you don't know what you are looking for, check for obvious gear damage. After that, you want to look at the blocking rings and the dog teeth on the gears. The blocking rings should have a pointed shape with flat sides JUST like little monopoly houses. The dog teeth will look somewhat the same except the side taper in the closer to the gear body you get. If the dog teeth are rounded over, the gear will gring when you try to shift. Check the inside ribs of the 1-2 slider and the 3-4 slider as well. FInally last thing to check is the mainshaft snout as those like to get chewed up from time to time and will cause noise in every gear but 4th. You need to pull the input shaft to check it and this will require removing some parts. Might want to download the T-5 manual for this as it would be nice to see how it goes back together.
To put it back together. Line up the shift forks and drop the cover down offset to the pass side as you took it off. An inch before it hits the tranny case shift it over to the left and drop it down all the way and bolt it in. Then silde the tailhousing on with the shifter block set up with the ball and spring under int he neutral position. SLide it in, bolt on the tailhousing and drive in the pin.
Pretty easy junk really. T-5's are an easy trans to rebuild