W124 sedan owners - body rust problems

Hi, All

My W124 sedan is now going for 10 years and I have two rather troubling rust spots on an otherwise sound body :

Problem 1 is at the bottom of the A-pillar, driver's side (euro car), right where the A-pillar joins the floor of the car. The rust appears to be at the joint between the sheet metal forming the A-pillar and the sheet metal forming the side of the car (the same metal that forms the door sill). There is no rust at any of the door hinges, fender, etc.

Problem 2 is the B-pillar at the passenger side. Exactly the same area (i.e. the sheetmetal forming the B-pillar where it joins the sheet metal that forms the side of the car - the same as the door sills). There is no rust at any of the door hinges, fron door lock, etc. on the B-pillar.

I am curious as to where the moisture that would cause this problem would get into the car. I have no current water leaks into the car and the area remains dry, even after a wash (apart from the spray entering between the door and the fron fender, no spray entering between the passenger side doors). I had the chance to remove the trim on both B-pillars and I did not notice any other signs of dampness or bubbling paint, etc.

I have not had the opportunity to see a dismantled body (i.e. able to look into the cavities at the floor or at the roof, etc.), so I have no idea at where to start looking.

I really need to fix the areas, but without knowing where the source of the moisture is I'll be wasting my time. Not notiving any new dampness might indicate that the system has been cured (i.e. a blocked drainage hole has unblocked - not that I know where they are BTW ...)

Any help will be appreciated !! I trust my explanaition of the affected areas are clear - I do not have ready access to a digital camera (yet ...)

TIA