Don't kid yourself. When we built our home we were told Moen would warranty all fixtures as long as we owned the home.. Sign us up right.. Not the case at all they have many restrictions and reservations to get around their "warranty" and they do change styles as the fashion dictates so you have to replace your entire fixture anyway. I have been in my home 20 years and they do not have all the parts available because they don't manufacture that style anymore.. So I have to replace two fixtures if I want everything to look good.. I will say too that Moen has the worst customer service I have ever dealt with..

Old galvanized pipes have a finite lifespan. If you repair this leak, you have a good chance of it developing another leak in another location. The only good solution is a complete pipe replacement. The major expense of a pipe replacement will involve the digging of the trench from the meter to the house. This is an area where a DIYer can save some money. Have the utilities companies come out and mark the location of the pipe and any other utilities going to the home. Then you can choose a route parallel to the current pipe but just far enough away from it that you aren't disturbing it. You can rent a trencher (Maybe $200) and hand dig the larger access points at the meter and house. Then you can call a plumber to lay the pipe and make the connections. If you are not physically capable of doing this, then do you have any family or friends that would be? Church group? Scout troop? There are usually community resources that can help you to figure out what you can do here. The worst thing you can do is to ignore the leak.

Not an expert here, just a homeowner with a similar experience...water on our windowsill after a heavy rain, but not always... just sometimes. It wasn't a problem with the window, or the flashing, or the roof above the window. From what we could tell, the problem stemmed from an upper roof, that dripped onto a lower roof that was above the window. The heavy rain would come off the upper roof and splash onto the lower roof with such force that it was bouncing back against the house clapboard. We're guessing that the water was somehow getting behind the clapboard and following the easiest path downward, by gravity, until it came out at the trim at the top of our window and dripped onto the sill. It took us quite a while to figure this out (and it is all really just a guess anyway), but the problem was solved when we put a small section of gutter on the upper roof. No more dripping water... no more leaking window. Water is funny. It may not come from where you think it would. During a renovation a few years ago, we had a heavy rain before a small section of the roof was entirely finished. Third-story roof, but the water leaked through a doorway in the middle of our first floor... nowhere near an outer wall. I hope this helps!

A good example of why you don't buy a house with zero setback on one side. Some basic info adding on to what Suzi said above. Stucco walls are only resistant to water. If there is no eaves protecting them from rainfall or if there are winds causing rain to hit them, they can get fairly wet inside. They have a space behind the stucco and any water that penetrates flows down the inside and out the weep screed. Soil needs to be 4" below that and the ground needs to slope away from the house at 5% minimum. 2% is allowed for a hard surface. If the project had a geotechnical report, it could make additional requirements. I guess that is a long preamble for my next statement, which is that the weep screed is there to get water out of the wall from rain and maybe some spray from watering - not drip watering. His ground level better NOT be higher than your cement slab. Clearly, there can NEVER be standing water above your slab level. He is totally wrong about his liability based upon what we see in your information, limited as it may be. Even without the zero lot line variable, it is routine large damage payments for excess watering, sprinkler leaks, or changes in grade drainage issues causing problems for downhill lots. Also, do your eaves hang over into his property? Are you in a HOA? Edited to add: I noticed this in a forum dedicated to old houses. Stucco houses built before about 1980 or so probably don't have a weep screed at all. Is this an "old" house, whatever that means.