Check your weather membrane. Most likely is weather membrane leak already.

It's like rubber, just pull out only.
I managed to pull out the rubber without hassle, but the electric connector socket damn hard stuck on the bulb, I think last time used more than 30 mins just to pull that socket out...

I replaced mine with book wrap LOL

Need to cut and UHU some places. It's time to get creative.

You'll need new bitumen as well to stick them. I just UHU all the way and make them one time use.

Search for black auto sealer and use to seal those back can already. My UHU is ajaran sesat.

saw too many people got this problem in Gen2 club group on FB. the problem lies in your weatherstrip seal or the rubber thingy at the edge of the door. it will eventually become cracked and will let rain water into the cabin. get it replaced  before you got any water damage.

your door plastic looks fine. but if you need to replace it, any plastic would do. i saw someone use black rubbish plastic bag, some even use plastic bag that comes with 10kg rice. don't use UHU glue. what you need is some black butyl rubber tape.

Bendix quite nice for me. But handbrake should related to your rear wheel brake. I suppose you need to get it serviced and adjust hand brake cable?
Just use any normal Osram or Phillips bulb. Cheap to replace. I tried LED and doesn't do good for opposite car. Change back to normal Halogen bulb. When need extra illumination I just put high beam.