Be aware that this piece has been customized to fit for each individual E9 at the factory. Incidently this fact made me love the hand made E9 even more! It is very likely that a Replacment piece from another car may be slightly too big or shorter the end of the piece to the back of the car.
As you know it is a solid brass core chromed piece!
My advise is to fit it to the car first before you send it for chroming! The tail end of the piece meets the bottom of the drip rail and if the replacement (donor) piece happen to be too long it can be filed the edge and fitted before you send it for Re-chroming ! Also there is small screw that secure the front of the piece to the body. make sure you place the screw in it. It is at the front where it mounts to the car! Re-chroming can fill up , or cover the small screw hole! W&N sells the curved (hockey shape) interior rubber ! The felt can be made from available glass shop squeegee felt and riveted very closely as original.
The lower u Channel rubber(3mm tall) that sits between the piece and the painted body is also available from both BMW as well as W&N sold by the meter . Make sure to cut this rubber piece slightly longer as it shrinks a bet. You can always cut it shorter if after few months of it sitting on the car if need be. Remind the body shop not to pull or stretch the rubber when they install it...
Best wishes !