When i purchased my 159 it had the usual water on door sills problem.
Just in case anyone else who has this and is struggling to get their head around it i though id just post a couple of pictures i took that clearly shows the problem.
Hope they help!
Incidentally this problem is almost identical to the leak i had on my mk 1 Seat Leon. In that case i went to the seat dealer and before i could even finish my sentence the parts man knew what the issue was and got me the improved butyl rubber sealing strip to replace the foam original. So when i discovered this on the 159 i popped to my local AR main dealer and asked if they had heard of this problem (showing them the photos) and to my surprise none of them had seen the problem before! Mine is an 07 so maybe AR changed the material on later models? Seat realised this issue back in 2001 after all.