It will be this problem...
http://forum.bmw5.co.uk/topic/116098...in-water-leak/
Essentially the bonnet hinge drain then has a drain down to this area. Now the actual firewall panel is the same for LHD and RHD vehicles. For RHD they take both holes out instead of just the RHD for the steering column. The hole left where the LHD steering column would be is then covered in a yellow grommit.
Unfortunately this area can fill with rubbish and then eventually not drain properly. In so doing the yellow grommit will fail. Some people put holes into the insulation panel to allow it to drain better others just remove it now and again.
The reason for the rear first on the passenger side is because the foam backing up front is thicker and the rear is thinner.
The yellow grommit part number is somewhere in that thread as well.
You may be able to reach down from above and remove it and clean it as well as look at the condition. Other go from underneath the car to do the same.
This potential issue can cause problems on anything sharing this chassis (F01 and the other versions, F06,F07, F10,F11,F12,F13 and from memory the Rolls Royce Ghost, Dawn and Wraith share a similar solution).
5' F07 GT (09/2008 — 06/2013)
5' F07 GT LCI (08/2012 — 02/2017)
5' F10 (01/2009 — 10/2016)
5' F10 LCI (08/2012 — 10/2016)
5' F11 (01/2009 — 06/2013)
5' F11 LCI (08/2012 — 02/2017)
6' F06 Gran Coupé (05/2011 — 02/2015)
6' F06 Gran Coupé LCI (05/2014 — 12/2017)
6' F12 (10/2009 — 02/2015)
6' F12 LCI (05/2014 — 12/2017)
6' F13 (04/2010 — 02/2015)
6' F13 LCI (05/2014 — 10/2017)
7' F01 (06/2007 — 06/2012)
7' F01 LCI (05/2011 — 05/2015)
7' F02 (07/2007 — 06/2012)
7' F02 LCI (05/2011 — 05/2015)
7' F03 (04/2008 — 05/2012)
7' F03 LCI (01/2012 — 03/2015)