I managed to get this working, so posting back how...
I changed my filter for day of the week, to a pages: i.e. one page per weekday.
On the map with the marks, define a highlight action.
- Run action on 'Select'.
- Source and target is the same: the map worksheet.
- Target highlighting: selected fields: select the unique mark identifier that keeps the same regardless of the day chosen
Then I also defined a filter action.
- Run action on Hover
- Source = the map sheet
- Target = a worksheet with week on week detail for the selected mark (client)
- Target filter: selected fields: added the unique mark identifier (i.e. client code)