Rust inside seat tube leaked orange water into BB shell. How to prevent from recurring?

I got home from a bikepacking trip with my chromoly frame Breezer Radar X (with lots of stream crossings), pedaling had sounded a little weird in the BB area, so I took my BB out and orange water oozed out from the BB shell. This can't be good for the BB, right? I'm guessing some water had pooled up in there entering from the dropper post routing port then leaked into BB shell. BB shell does not have a drainage hole btw.

Next, I removed the seatpost and saw this. It seems there's mild rust inside my seat tube including at the very bottom in the BB shell/seat tube joint.

The rust in the middle/lower part of the seat tube isn't super concerning to me, and the stuff at the very top where the seatpost contacts I can probably just scrub away and apply grease there.

My question is what can I do about the rust at the very bottom. I don't want it to get worse, and ideally I'd like to prevent the orange water in BB shell situation from happening again. Here are some options and questions I've thought of.

• At the bare minimum, plug dropper routing hole and grease upper seat tube to help prevent water entering.
• I purchased a can of aerosol T9. Can I spray that directly on what's already there? Or does applying it on top of this much rust not really work?
• If I end up hitting the whole inside of the frame with T9, would it then be a bad idea to grease the seat tube?
• I'd like to avoid the T9 route if at all possible. What about trying to smear some grease down there to cover that rust?
• liberally grease BB shell and forget about it?