I dont find it that easy to break traction in the wet, with stock gen3 power.
Yes it will break traction in first and second but you have to be really hammering it.
In the dry it is glued to the road.
 

Thanks Jay!!
The PP rear corners have been fitted since then, and the exhaust tips have changed.
I look forward to having some more nice photos taken very soon, hopefully with Work Equip wheels

I picked up the second hand LSD E153 box from Gorilla last night, and dropped it at Gearbox Express this morning so they can inspect it. 
Having just talked to Gearbox Express after they pulled the box apart, here is the latest news:

- The synchros for 2nd and 3rd gear aren't looking good

- The little gear on the electronic speedo sender is broken, but I guess that doesn't matter because I'd be retaining my mechanical speedo anyway

- There is no 'hex bar' visible when looking into the stub axle holes in the gearbox, which should imply that it doesn't have a factory LSD, but Gearbox Express are convinced that it has some sort of LSD

Regardless of the LSD, the pricing is another major factor.
They said it will cost $250 if they simply replace some seals and put it back together as-is, which is a reasonable amount.
However, if they were to fix the synchros before reassembling the box, it would cost a total of $1400 - ouch!
Also, both of the above options are not including the cost of the box itself from Gorilla Industries.

I can still get my original gearbox repaired if I want to, but it wouldn't have the benefits of an LSD or revised synchros.

So much to think about! lol

Given the cost of fixing the synchros in the second hand box, I am certainly considering that idea.
I could look for another second hand box of course, but it wouldn't be worth the hassle when it could have the same issues or worse.

My car is still in the garage and the original gearbox hasn't been removed yet for a proper inspection of the problem. My mechanic will be doing that, but the car will need to be towed to him, and I don't want to leave the car with him for longer than necessary.
I still think it's very likely that the 5th gear shift fork has broken, and possibly damaged some part of the gearbox casing, and therefore the fluid leak is probably gearbox oil.
I guess it would probably cost a lot less to fix the shift fork on my existing box rather than fixing the synchros on the other box, but I still have to consider the LSD situation (after confirming what type of LSD the other box has, if it has one at all).

Bummer to hear that... I'd put the E153 box back together and not worry bout it.  That price is ridonkulous - $1400 for new synchros + buying price + not knowing whether it has an LSD or not. 
Then pull out your old box and it might be cheaper going down route MRturbo suggested - Quaife unit with your old gearbox.  Guess it depends on how bad the damage is...

Its a pitty you didn't look for the hex bar before you dropped it off at the gearbox shop.
Does this new box have the upgraded synchro design in it? That would prove its at least a late model E153 box.