I am a licensed plumber< eighteen months ago I completed a basement remodel, adding a new bathroom and kitchen. I added a hot water recirculation line, with a brass watts pump, in the past two months I have had three different 1/2" 90's develop pin holes in them. the holes are in the fittings themselves not the joint. when I did the job the home owner did not want to replace their 20 year old water. a month ago I replaced the water heater. wondering if anyone has had something like this occur to them, or what the issue is.