replacement sill

[jesustrip]

Hi Folks, i have a 318i 1995, had it for about 6 months.
Ive a problem with the driver side sill, under the back passenger door a small hole had appeared, upon prodding n pocking around with a small hammer i now have a section of the sill which is around 15 - 20inches long that has totally came away.....somebody has done a dodgy patchup job and stuffed a dishtowel inside the sill before sealing up a hole with god knows what.
Anyway.....whats the best solution......repair or replace the sill????
Anybody tackled this before on this forum?
The sill looks like its moulded to the car (this is my 1st bmw.....)...been having a look round on the internet but cant find any info.
What to do?

Cheers for any help