What is likely the problem is a leaking check valve which is on the "other side" of the dispersion screen and is evidenced by a steam leak through the dispersion screen.
The dispersion screen screw threads into the check valve body. Does this agree with the pdf you have of the machine? You might try flushing some descaling solution through the machine and that, by itself MAY cure the leak. If not, then keep in mind that this little valve body is sometimes difficult to remove and requires a large stubby screwdriver probably with the blade fattened a little to give a nice tight fit in the brass body of this check valve.