This is a problem for many. You did not say what part of the country you are in, in the West we have this happen often due to the soil condition and the way in which the pipe was laid in the ground. Per code sand should surround all pipe underground.
The leaks in your walls could be a water velocity problem. How large are those return pumps? Is it always hot water? Does the return line come back to the boiler room 1/2″ in size? What is the water pressure? Does it increaese at different times of the day? Is hot different pressure than cold?
There are alot of questions to be answered. With 150 leaks in the system it seems as if a repipe would have been discussed by now.
There is also a company that relines the existing piping system with epoxy. Beware that this technology is new and far from foolproof.
The epoxy has a tendency to not fill the pipe evenly and or not cover the piping at all. It is, in my mind an expensive experiment.
The Local Plumber
Tustin, California http://www.TheLocalPlumber.com