T-5 dilemma

This question is for my 1991 GT with 281K miles. I think the transmission is finally getting a little worn in the synchros. Around 30K miles or so, the transmission was worked on by the dealer under warranty. I don't know if they replaced it or just took it apart and fixed it. It was grinding while shifting. This was after the car was stolen and recovered.
Anyway, I have had no problems with it until the past few years. A little grinding, sometimes, and hard to get into gear, sometimes.

My dilemma is:
A) Rebuild it myself. I have an F-150 to drive in the mean time, but much prefer the Mustang. Better gas mileage, easier in traffic, for fun, great looks, and so forth.
B) Buy a used/rebuilt unit from flEabay, (knowing it is either heavily used or not actually rebuilt), run with this tranny while I take my time rebuilding mine,
C) Just buy a new unit and be done with it. Maybe also rebuild my original(?) unit in the mean time.
D) Take it out and haul it to a local shop for a "rebuild"

My preference is to keep the car original, and I have been really good about this, but I don't know if the tranny was actually replaced and the original one long gone now. I don't really have a problem with having an extra hanging around, except for the space it takes up. Maybe with option B, sell the used one when I am done.

One of my concerns is when I get into the rebuild, finding I have to start replacing gears and other parts. This adds to the rebuild time.

I have no problem diving into the tranny. I have done MANY engines in the past. (Burnishing my bona-fids here) My first (high school) car was/is a 65 Mustang, which I still have. My current car, the 91 GT, I bought new, (and it still has the original clutch in it, 281K miles!!!). I feel confident I can tackle anything outside of an automatic transmission and some body work (but I am moving into that arena). I have watched several T-5 videos on youtube. What I am missing is how to judge how much wear on a gear is too much. What can be used versus what should be replaced. Left to my own devices, I would replace ALL gears just to be sure. This slippery slope ends with a new T-5.

I'll look into the T-5Z. I don't race the car, or drive her hard anymore. I have others for that. I think you would call it "Spirited Driving" on occasions. Don't know if I am sold on the ratio changes yet.

I want to stress that my transmission has not been abused. I have developed a method of RPM matching which helps the shifting without grinding. I get grinding sometimes, but (hopefully) not too bad. Anyway, I have no problem with ALL new gears.

Where is the best place to get good quality parts?