Rear door

Please can anyone offer any help ? My 850 estate has started to corrode on the black metal strip just below the boot glass. Has any one ever replaced it ? is it complicated ? or is it a main dealer or body work specialist job ?

The strip slips up under the glass it's very simple to remove

strip on boot 

thanks for your advice, can you please give me an idea what's involved and how to do it ? or is there a search forum i can look at, thanks !