Both the A/C compressor and alternator utilize rubber isolator bushings at their mounting points. When they get really worn out, the belt pulleys don't align very good. There are a total of 8 bushings used for both accessaries. I just went through replacing them about a week ago on our 90 740. I found it easier to remove the air cleaner box and intake duct to get better access to the mounting bolts and hardware. I unbolted the alternator and swung it back out of the way (carefully with wires still attached) to gain access to the top of the compressor. I also dropped the splash shield under the car to get at the lower compressor mounting bolts. Pay attention to which direction the bushings slide in from - some go in from the front, some from the back. It's not too bad a job to do - took me about 1-1/2 hours, and I'm not a "pro".

I believe FCP Groton has the bushings for less than $2 each. I had to pay $3 at my local supplier. The dealer wanted $10+!