V8 Auto Gearbox Let Go.

Hi. Does anyone know of a good recon gearbox specialist in the essex area as i have lost the third and reverse gear. I have visited my local garage and they have quoted me £700 to replace and fit a reconditioned unit. I have considered buying one off ebay but i could end up with one as bad as my own so any advice would be much appreciated.

Cheers.

Simon.