[acidrain]

Probably didn't get all the prep chemicals out of the holes before ano.
Try this:
Prep and polish your parts normally (strip, rinse, de-smut, rinse, dry, polish).
Use lacquer thinner to get every bit of buffing compound off. Pay special attention to the holes. Use a toothbrush and small bottle brush if possible (the drug store sell really tiny ones for washing measuring syringes).
Degrease in your heated SP degreaser for only a few seconds, and immediately dunk in your rinse tank. Check for water break, and repeat if necessary. Once they pass WB, spray rinse the parts and especially the holes.
BTW, there is a good chance the welds will not look the same as the surrounding areas unless they were done using the same alloy filler rod.