[Hauteknits]

Hey guys, 3rd gear just went out on my 2013 E93 335i. I currently have the GS6-45BZ (THD4), and I'm in the market for a new transmission. From what I've researched for a while there are NO replacement parts/rebuild kits on the market. I've narrowed my choices down to 3(ish) options

1) Simple swap, find another THD4 or THY8, requires finding a completely functioning trans for a good price
2) Rebuild, buy a trans that has some issues with a different gear, and Frankenstein together a working trans. However, heard that cracking open the trans is hard as shit and not even dealers do it
3) GS6-53BZ swap (n54 variant), apparently the 53 is a lot more durable than the 45 and (supposedly) people often swap to it. To pull of the swap I'd need a new clutch, flywheel, shifter linkage, shifter bracket and driveshaft.

What's the best option here?
Also in AZ, so finding used trans out here isn't super easy, likely going to have to go to CA to grab something