Here's an excellent video tute for replacing this
BFG94 transistor, by psxnet on Unlockers:
The problem with this component in the past has been that peeps have only been able to buy it in a minimum quantity of 6 off. If you've sourced yours in the UK, and can get one only, then count yourself lucky!
But state where it's coming from, just in case another member lives nearby and can collect in person and post it to you cheaper. For example, Cricklewood Electronics do it as a one off @ £2-00 + VAT, but P&P is £3-00 + VAT
Cheers- AL