Thanks Prime_Tech for your post.
I can confirm that by following your advice and downloading the March 2014 Web Camps Training Kit installer from https://www.microsoft.com/en-gb/download/details.aspx?id=36393
then by manually selecting to install the .Net Framework version 4.5.2 components
My dashboard now reports that the drive is healthy.
It may be possible to just download the .NET Framework version 4.5.2 and install that but the Web Camp Training Kit installation did report that it has installed some IIS components too. I think it is unlikely but perhaps the fix could be related to one of these IIS components that the Web Camps Training Kit installs.
I hope this helps someone.