I have an ongoing gearbox related problem for which I would be very grateful for any advice. I have paid over £350 and still have a broken gearbox, with neither party accepting responsibility.

Over 5 weeks ago now I paid a mechanic to fit a used Renault Clio gearbox I bought from Renparts. It was the second one they sent out, as the first was damaged. So, as it turned out, was the second. However, the mechanic insists that it was impossible to tell the second was damaged, and the supplier says he should have been able to tell, and therefore won't pay the labour costs.

The gearbox, now fitted, only goes into reverse, 1st and 2nd gears, with 3rd, 4th and 5th not engaging.

It looks like I'm taking somebody to court over this, but the question of who is dependent on the answer to this one:
Should the mechanic have been able to determine that the gearbox has no working 3rd, 4th and 5th gears prior to fitting it?

Any help is much apreciated.