Yesterday I had the unfortunate pleasure of becoming one of the many people who have had a gearbox fail.
Coming onto a dual carriage way in 3rd gear accelerating from around 40mph the car jumped into neutral - there wasn't any loud bang just a sort of dull thud sound.
I coasted onto the hard shoulder and had a look under the car. It doesn't look as if it has a punched a hole in the bell housing but there is oil leaking around the gearbox area.
Now my car will drive in 1st and 2nd gear and Reverse but makes a sound like a spaceship and 3rd, 4th and 5th are completely gone.

Now my ST is supercharged so rather than stick another standard box in it just for it to explode again i'm looking for an uprated box possibly with an LSD in - maybe the IB5 box from Jamsport with the RST dif. for example.

Anyone been in a similar situation and able to give me the bad news and say how much this is going to set me back?

Sorry to hear the news, certainly a new box from Jamsport or a rebuild by a professional with a LSD will sort you out

An LSD won't stop it from exploding again though.

Without any knowledge of what other gearboxes will fit (e.g MTX-75) you may want to look at people like Burton engineering as I think they do a Quaife gear set for the IB5 which can handle a lot more power/torque.

check out pumabuild they offer a Quaife gear set and LSD

http://www.mst-developments.co.uk/contact.htm
Give these a ring, might be able to help you out, rebuilt ST boxes with lsd's.