if you drain the oil and see copper in the oil i would say your synchro has gone..
and looks like you have to remove the gearbox and strip it apart to see how bad it is.. maybe its best to get a second hand gearbox from the wreckers.. ps make sure you get the right ratio. if you not sure let me know i might be able to help you.. check the LHS of the gearbox to see the number on the box it starts with ty752vb3fa for example.. hope that helps..