Confusing door trim left over on re-fitting interior

Hi. I've got a 1973 T2 Westie and took the interior out last year. Putting it all back together now but have a part I can't remember how to re-fit. It's a length of flexible plastic about 78cm long by 4cm wide and has a "L" profile (see pic below). It was somewhere on the top of the sliding door near the curtain rail... any ideas please? Also, what is it supposed to do? Cheers.

 

Can't see picture, but it stops you banging your head on the sliding door opening.

 

correction.... it softens the blow when you bang your head.

 

...and irks you because it's shrunk and gone wavey over the years. I binned mine, but it was disgusting.

 

yep, I didn't refit mine as it went all wavy davy and yellower than a chainsmokers teeth.

 

Cheers guys... mine is in pretty good nick although had gone wavy until I left it in the garage with a pile of stuff on top! Any ideas how it actually fits on?