Rust on bottom of driver's door trim - 95 525i

[Russell]

I just noticed the body color painted trim (95 525i) on the bottom of my driver’s door is showing a bit of rust on the inside of the door and the trim. No rust visible on the outside of the door. I sprayed "Super Lube", a synthetic water displacing lube in the groove along the inside door edge on all four doors. Hope that slows it down.

Question. Is there any sort of rust stopping spray/paint I can use in this grove to stop the spread of rust? I have heard of POR-15 and the Eastwood encapsulating products.

If bodywork is needed, what is usually done and what parts are needed? Is it just the trim that is the problem and simply replaced and repainted or is there rust on the door bottom and the door needs to be repainted. If so, that usually involves paint matching on the entire bottom of the vehicle. Looks a major deal.

Archives offered some advice. However, i just wondered what the current thinking is.
TIA