My gearbox is making a very unpleasant grinding sound whenever I change into 6th at any speed above about 55mph. I'm pretty sure the synchromesh is going/gone but the next step is not really clear to me. I see three options:
 
	 
 
	1. Change the gearbox oil in the hopes that I can buy myself some more time
 
	2. Pay for an expensive repair on the gearbox
 
	3. Find a second hand gearbox from somewhere and get that fitted
 
	 
 
	Has anyone else had a similar problem, if so, what gearbox fluid should I buy? And if that's not going to work how much do you think the repair options are going to cost?
 
	I live in Kent and my zed has 38k miles.
 
	 
 
	Any help very much appreciated!