I'm running Fusion Version 4.1.4 (900582) and have added the additional line to the vmx file as Brian suggested but to no avail. Is the mks.vsync parameter supported on my version of Fusion or am I going to be forced to upgrade to V5 to resolve this problem. Thanks in advance for any guidance offered.
BTW disabling 3D acceleration and changing the mouse gaming setting solves flickering in single view mode but, as someone else has already said, doesn't help with Unity mode which remains unusable.
Update: Think I've answered my own question. I've installed a trial version of V5 and both single and unity views work perfectly - no flickering. The question now is whether I want to spend EUR44 to get something I thought I already had.