when ever i put it into 3rd gear it scrunches going up or down all the other gears are fine i have a short shift gear change fitted will a change of gearbox oil get rid of this or not its like there is no syncro

 

if the gbox has been filled with fully synthetic oil it may cause the syncros to grind.

Suggest you try Castrol Syntrax - semi synth as it seems to cure notchiness (did on my car)

 

cheers m8 ill try that