Helpat

Hi,I'm hoping someone can advise. I've got a 2005 skoda fabia ambiente estate. Water is leaking in seemingly from the rear door seals. Ive done the fix once before with sealant but this has last 12 months. I went thru the carwash this week and water came pouring in thru the top corner of the door nearest to the seatbelt fixture if that makes sense. If I wanted to replace the actual seals is this an easy job and where would I get the correct seals from? I'm thinking of re-doing the sealant again using plumbers gold but could I use this to repair this new leak point in the top of the door?