There are basically 2 components to each side. The rear covers are short and black and can be refitted once removed. The long ditch finishers that run up to the windscreen are colour coded and you’ll probably break some clips in removing them but they are usually refitable with some luck and a tube of Tiger Seal at the ready just in case.
My channels were pretty grime filled once I removed the ditch finishers but as I was fitting roof rails too, these held the ditch finishers in place once they were screwed down.
I strongly suspect water will get under the ditch finishers as they are not water tight so if you do remove them, make sure you have sealant/Tiger Seal/panel adhesive on site so you can seal them up once reinstalling them.
Whilst you’re in there, it just might be worthwhile ensuring the two forward screws are tight + sealed up as this will be a perfect place for water ingress. There’s a photo in this thread:
Linky
You can buy the components separately, well, in pairs but they are hellishly expensive and will cost you over £100 per side, which may sound reasonable but is a rip off for what they actually are. Also, you’ll only be able to buy black coloured ditch finishers as they are not available as colour coded items.
Take your time removing them ( they just prise up ) and have some sealant ready just in case and you’ll be fine.😉
This video is also worth a watch before you start:
https://youtu.be/21JNNXJ_dSY?si=tjxSnLAcZUpgc0NW
Also worthy of a read, paying particular attention to Note 10 is this:
https://accessories-instructions.landrover...y/G2011166