Nissan never again

I drive a Nissan 370z and have been taking my vehicle to Melrose Nissan for more than tree years. Three months ago I saw that I have a leak on the seal of the prop shaft that goes into the deferential. I honed and made a appointment for the repair. I had to wait a month for the spares to arrive. On the day of repair I waited for the car for it was supposed to be a quick job, When I received my vehicle, I noticed that it felt that the handbrake was pulled up and I complained. I again went back to Melrose Nissan and complained, I was told that the differential nut is been tightened to tight but it will work it self out. Three weeks later I had a hum at the back of my car and I thought it was a wheel bearing. Again I went to Melrose and I was told it is the deferential. I could not believe it for I never had any problems before, so I approached a gearbox and differential company and told them what happened. The fact that they tightened the nut to tight caused that the differential failed and got damaged I was told by the company that Nissan uses for the repairs of their differentials. My vehicle has now been standing for two months seeing that Nissan does not have any spares. Saying this, and that is where it ends, I the client had to source around for spares and see if I can get a secondhand differential seeing that Nissan does not have in South Africa or Japan. This would have cost Melrose Nissan R 35 000 to fix if they got the parts from Japan. Last week I got a second hand differential from a can that only had 35000 km on the clock for the price of R 12 000. It has been four days since then and still Melrose have not paid for the differential, how long does Nissan South Africa want us to sit without our vehicles they sold to us with a promise of spares. Are we just good to the dealerships when we buy our cars for commission or are they the same when we need our cars repaired this does not look like it. I will not buy any Nissan product again for the service from Nissan does not exist seeing that not South Africa not Japan has spares. There are a lot of models that have the same problem under Nissan, don't buy a Nissan product.