Call the Distric Service Manager. They are there to solve situations like this. If you have a reasonable doubt, which you do, I think you'll find they will work with you. Call the dealership, ask for the service department, as for the name and telephone # of the DSM.
-Was the "bad" pulley a new one (came with the new alternator)?
-The crystallization issue should not be something that you, the customer, bringing your car to an authorized dealer, should have to even determine let alone deal with.
If it is a bad pulley (very unsual) from MBZ they will definately stand behind it. You have a warranty on the work done. If it is a dealership installation problem, this will quickly come out and they will be obligated to take care of the whole thing.
Give it a try.
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)