I replaced my fan bearing bracket + smog pump idler @ 120k miles and now at 145 k miles the A/C bearing is in need of replacement.

I would say if you hear strange things in there just go ahead and replace them all (fan bearing bracket, smog pump idler, A/C bearing, 2 idlers). They usually fail within a very short interval of each other anyways and the parts really aren't that much (with the exception of the fan bearing bracket).

Dedicated idlers you can get @ the Benz dealership, the smog pump and A/C pulleys you can get the bearings pretty inexpensively at www.bearingsdirect.com provided you have the dimensions (which you can easily find on eBay if you know your smog pump and compressor model).