^this exactly.
I bought a used 833 from a wrecked dart. It looked great inside and out, very clean and exactly what it was advertised as. I pulled the side cover, all the gears were consistent in color - no blue (which would indicate heat or lack of lube). It felt smooth, engaged all gears, etc.
Once installed, it worked, but the second gear synchro would very slightly grind on downshift each time, and often during a full throttle upshift. Would still shift though. Then came a horrible noise that got progressively worse over about 30 miles. The input shaft bearing was toast.
For about $200, I rebuilt it at home with new synchros, gaskets, seals, bearings, pretty much everything. Got all the parts from brewers, including their trans rebuild lube/grease. It was super simple and took all of about 4 hours. The hardest part was removing the reverse gear, for which I made a contraption from allthread and some pipe and washers (search around and you'll find some pictures of such a contraption - it's commonly suggested for anyone taking the trans apart). Cost about $20 and took less than 5 mins to get the gear out from what I remember.
The hardest parts are the cluster shaft roller bearings - which really aren't that hard, and the rear bearing snap ring which can be fiddly to remove and install properly.
So long as the gears show no signs of rust, pitting, chipping, heat, or other issues I'd grab it and plan to put new bearings in while it's out of the car - installing the trans into the car is by far the hardest part of the whole job!
