Long-felt

They always satisfy a long-felt want - on the part of the professors; and they seem to be "fillin'" to certain "aching voids" that gather in to fill the classes.

Source: wiktionary

Here Plaintiff says that the St. Germain patent supplied a long-felt need when Plaintiff itself, an aerosol valve manufacturer, has never been able to give the public one single St. Germain valve structure.

Source: wiktionary

The longest-felt need in computers has been for an economical on-line memory where vast amounts of information are almost instantly accessible.

Source: wiktionary