'90 300E 4mat diff. replacement
 

I need to get the whiney diff outta my car, cant take it anymore. I've tried the heavier oil idea, to little effect.

I want to know if anyone has any advice on used / rebuilts and how pricey the replacement is apt to be.

I see many used diff's available on Car-part.com, $250 -400 on avg....but I'm worried that the problem will just be replaced with another one. One problem is that the diffs are sold as Carriers, which may or not include all the new parts I need to be done with the whining.

Thanks in advance.