BMW Repair: New or Rebuild Differential ?, ring and pinion gears, bmw repair

Question
I have 1989 BMW 325i 2dr automatic with 280,000 miles. Last year I changed and rebalanced the drive shaft.

Now, I when I put the car in reverse, I can hear a loud click. When I put the car back in forward, I hear the click again.

I took it to a BMW repair shop and they told me, the differential is wearing out and to replace it will cost $2,300.

I called a shop that rebuilds rear ends and they said that they can do it for $600.

My question is can I be secure that this repair will last? The BMW repair said I have approx 6 months before it dies.

Answer
Carl,
 The #1 thing you have to learn here, is that the dealership will tell you anything to get you in their doors to pay them.  You need $2,300 worth of work done to your car, of course "you only have 6 months before it breaks,  so bring the car in here tomorrow and pay me, even if it isn't needed".  What is hilarious is that they gave you a time frame that it will fail!!!!  How does this person know that it will last 6-months and not 1 year?  Where did he get this info???  It just goes to show you that they are greedy and will take advantage of anyone they can.

 I DO NOT like dealerships, as they rarely fix a problem right the first time, (read posts by other people here) but they never fail to overcharge you for their work.  Also, I deal with dearlships on a daily basis, by selling parts to them.  On average they have a 400% mark-up on all of their parts.  So if you feel like paying 4-times the ammount for parts, and then their rediculous labor rate... be my guest.

 Now to the problem at hand, they said your whole differential is worn.  First you need to understand what is happening inside.  The drive shaft turns a gear inside the differential.  This is the pinion gear.  The pinion gear is connected to the ring gear.  This transferes the spinning of the drive shaft, to the forward spinning of the wheels.  Where your problem lies, is in the ring and pinion gears.  They have worn over the 280k miles, and have some play in them.  So if this is the problem, why replace the WHOLE differential???
 I would take it to a competent shop and have them put in a new ring and pinion.  While they are in there, they might as well do bearings an seals.  Thats that the other shop is doing (I'm 99% sure).  That's also why it only costs $600 to do.  

 I will say that BMW differentials are a little more time consuming to change than an american car (Rear wheel drive).  So thats why its $600 instead of $400 or so.  

 Carl, I hope for best, good luck!,
   Josh