ive just spent alot of my weekend tracking down 2 leaks on my eg6 and neither were coming from the light seals which is where i thought it was coming in. Might not be in the same places for you but mine were a bitch to find!
The biggest leak was ending up in my passenger side rear arch at the back and if you look at your fuel cap you'l see the little drainhole at the bottom, behind that drainhole has the two pieces of metal which make up the rear quarter ( cant see it unless you remove the plastic guard for your fuel pipe ) and the water comes through the drainhole, down onto these 2 pieces of metal which had no sealent and into the car!
Its the first time id looked in this spot since i got the car 4 years ago and couldnt believe it, either the sealent fell out or it was never there in the first place! Cleaned it out and filled it full of tiger seal, pissed down today and its dry inside
Second leak was a crack in the sealent on the rear drivers side, cleaned it out, tiger sealed, fixed!
Il get some pics up tomorrow because that spot under the fuel caps drain hole is worth checking out! I also didnt realise the 2 bolts which hold your fuel cap on is 2 direct holes into your arches, if they let water in then kiss your arches goodbye lol