2005 Corolla gearbox

[aidank]

I am the owner of a 2005 Corolla 1.4vvti saloon.  My gearbox is getting noisy at 200k miles, noteably roar at 50+mph.  it makes the same roar in all gears and pressing the clutch or taking the car out of gear doesn't change the noise.  Going around bends doesn't change it either.  Wheel bearings were done at 185k miles or thereabouts.  Noise has  gotten worse over the last few weeks, I have a feeling there is a bearing dying in the gearbox somewhere.  Oil was change in it few times over the last 19years, it was done at 70k, and at 150k and just last september at 190k.  I guess its time for surgery.  Indeed one bearing was done at 150k miles by a specialist who is no longer local to me.  

Im looking at getting a recon box and I have made a few phonecalls and they tell me there are a few variations of the box, apparently some have an Aluminium backplate and some have a steel backplate.  

Is there a way I can identify the box somehow and make sure I have the right one before mechanic start the exchange process.  No one wants to take on a repair job on the gearbox.  500ish for a reconned box with new bearings and seals, 250 for a box from a breaker, which may be no better.

The car is in perfect condition.