I DID check and there was no bar visible, so it must not be a factory LSD.

I'll go back to Gearbox Express tomorrow and get photos of the diff and the axle holes.

factory ones are viscous, i had my gearbox overhauled some time ago, and mine has got a Mechanical LSD in it now i remember the mechanic telling me it didnt need any special stub axle, its been a while so i dont remeber what was said.
but recoing a box will cost around 1.5k, the 2nd and 3rd synchros are very notorious for going on mr2 so i would def fix them in whichever of the box you choose to go with.
if the box has never been opened before and they say its got some kind of lsd then it has to be a viscous one.
if your going with viscous one its not a repairable unit and once its worn out it has to be replaced. mechanical clutch type ones can be serviced, problem with the clutch type ones are they never are quiet and will shudder a lot if the wrong oil is used in the gearbox, use the right oil for the LSD and the synchros will start playing up and get hard to engage, its a no win situation, so you have to pick one or the other(smooth shifting or LSD chatter) you can get them to a happy medium but involves a lot of headache trying to get the right amount of LSD additive into the Gearbox oil so that it still shifts ok but also doesnt make the LSD chatter. i still havent found that medium yet cause i gave up lol.
 
cheers

^ that's the reason why you go Quaife ATB - drives as quiet as stock, doesn't need any special fluid or additives, maintenance free (Life time warranty). Install and forget.

Viscous LSD may not be rebuildable, but they can last a long time. Mine was checked 15k ago when I rebuilt my box & it was still fine. 220k kms approx.

Verify that box & search for another IMO.

I went back to Gearbox Express this morning, and I can now confirm that the second hand box definitely has a clutch/plate-style LSD.
 
*EDIT* some photos and comments removed, sorry if that causes confusion for future readers of this thread!

so the gearbox rebuilders were wrong???, theres no way that box was factory sealed and had that in there.
that looks very much like what i got except my plastic/nylon ring is blue instead of yellow.
the TRD ones chatter less apparently. but i guess that depends on how tight the shims are in the LSD

purple5ive
so the gearbox rebuilders were wrong???, theres no way that box was factory sealed and had that in there.
that looks very much like what i got except my plastic/nylon ring is blue instead of yellow.
the TRD ones chatter less apparently. but i guess that depends on how tight the shims are in the LSD

They didn't say that they were 100% certain that it hadn't been opened, they just said that it seemed very unlikely because the transmission sealant looked and felt exactly like it would from the factory. That was before I mentioned the fact that Gorilla Industries got the box from Japan, and who knows what they do over there.
Does anyone know if TRD diffs were ever fitted as a factory option? I assume not.
It would still be nice to confirm if the diff is a Kaaz LSD or TRD LSD, or neither.

It probably is a KAAZ (Edit:clutch) unit in there (going by the plates and no hex bar).
TRD is mechanical and only aftermarket AFAIK.

I remember hearing a few years ago that there was a TRD viscous LSD available for the E153. From memory, someone took a close look at one & it was pretty much the same the OEM LSD. I wouldn't be surprised if it were a factory fitted option either.
 
Had a quick poke around & there's a few Gen3 LSD transmissions for sale on Ebay. Didn't look closely @ the terms, but if they can be inspected & somewhat warranted, wouldn't be a bad option at all.

DVST8R has now shown me a photo of his Kaaz LSD, and it looks *edit* very similar. 
 

MR2QIK
I remember hearing a few years ago that there was a TRD viscous LSD available for the E153. From memory, someone took a close look at one & it was pretty much the same the OEM LSD. I wouldn't be surprised if it were a factory fitted option either.
Had a quick poke around & there's a few Gen3 LSD transmissions for sale on Ebay. Didn't look closely @ the terms, but if they can be inspected & somewhat warranted, wouldn't be a bad option at all.

I don't want to keep trying my luck with other second hand boxes, because I'll always want to get them inspected, and unless I'm lucky and find one that needs no work at all, the inspection costs will keep adding up until I find one that needs no work at all.
EDIT: I just noticed that you said "if they can be inspected & somewhat warranted", but I don't want to take that risk.