I have a W reg classic about 84k on the clock, there is bad crunching between 3rd and 4th when accelorating, my friend said about the synchro and that it might be better to echange the gearbox for a re-conditioned one rather than a repair, advise much appreciated

 

stick some castrol syntrax g/box oil in it mate that sorted my crunch between third and forth!

 

The crunching will be the syncro. Generally speaking when the syncro is replaced serviceable parts that are worn in the box can also be change at a lesser cost.

Depending on where you shop the costs should be similar to that of a recon unit.