Harmony Boxer

I have a Harmony on a boxer base year 2003 and have noticed a problem with rust around the drainage outlet just below the glass window in the rear door which has caused a rust stain running down the door.


 Has anybody had the same problem and solved it without going to a body shop specialist, if so what filler was used and was it necessary to remove the glass and rubber moulding from the door, any help would be appreciated thank you