so "replaced" means that you, or was it a mechanic, swapped out your waterpump?
are you seeing any fluid that might be getting on the main pulley?
were not even going to suggest this, but of course you should already have a new belt. (theyre available everywhere and i usually buy more than one for backup) theyre not built to last forever. also use some CRC belt dressing to condition it prior to installation.
my alfa mechanic sent me to the autoparts store with a few numbers, then used the size that fit best for AC and sent me back with the unused one. and he was a dealership guy. so dont neccessarily get held-up by the records of available parts per make/model at most auto-parts stores.
hell, DDouglas was just telling us how his crazy *** had been running (maybe past 130mph, that viscious bastard) with a non-OE alternator, and no friggin retention arm/bolt.
his engine is toasted, mind you (and theres an alert within the alfa-community to not allow any engine parts to be sold to him until he learns to play nicely with his toys) but the moral of the story is that your Alfa is more flexible than it may seem.
try some belt sizes and see how it goes. she's italian... she can take it.