The nice thing about three-button mice is that they are brilliant at cut
and paste; Left button cut, centre button paste. You need to set it to
mouse-systems mode though. See:
a Mouse to 3-Button Mode
After decades of use the left mouse button micro switch may fail.
In my mouse I replaced this by a Zippy DF-03S-0P-Z, but a Zippy DF-P1L-0P-Z may work as well;