Fix and prevent corrosion on a bath tub drain?

I would replace it since the part is relatively inexpensive.

It may be easier to replace it, but if the issue is your water you may need to keep cleaning it. Here are some tips to help you. https://www.gc-plumbing.com/blog/2018/january/5-ways-to-remove-rust-from-tub-and-sink/

Sno Bowl toilet bowl cleaner, works every time. No matter how bad.

Before buying a new drain you could try getting the mineral build up off yourself. Good, old-fashioned, white vinegar will remove this mineral build up. You could soak a wash cloth in the vinegar and place it right over the drain. Cover it with plastic wrap. Let it set overnight. Then remove the plastic wrap and scrub the drain with an old tooth brush. Rinse with clean water. You may need to repeat this process.

Hello. I have the same problems with my bathroom sink drains. A build up of minerals both on the metal part of the drain and stopper and some staining at the lower edge of the sink right above the rim. The mineral causes the lowest aspect of the sink to discolor as well.

I have found that using WHINK Calcium and lime remover to eliminate the mineral stains quite effectively.

I thought my sink and stopper were permanently set damage stains but WHINK took care of it. I understand some chemicals like CLR are too strong but the WHINK has worked for me in my cultured marble sink in my satin sink nickel hardware without any damages.

It might be worth trying a chemical removal before considering a replacement. Hope this helps

Make a baking soda and peroxide paste if it is only build up. It looks like corrosion in the photo which would need to be replaced. Prevention would involve making sure it drains properly and water doesn't sit after each use.

The corrosion and build up is due to the finish being rubbed off. The drain just unscrews from the drain pipe. The four slots are for a special tool but I have used a pair of long nose pliers to unscrew it. I would first spray the drain with WD40 to penetrate the threads. Work carefully and slow so not to break the "+". It's only brass.

You can replace that part, you can find a replacement at Home Depot or Lowes

Try some CLR. if that does not work go to Home Depot or Lowes and purchase a replacement

I would replace it

I would throw it straight in the bin and have it replaced. We had a leak in the past due to a corroded drain in the house, and it was not a nice view. You had on one side my husband saying he can clean it up himself and me being so disgusted even to get close to it, let apart clean it with detergents. When it comes to a water leak repair, it's way better to call a plumber as they have the tools and the expertise. For every work you need to be a specialist to do, it's advisable not to get involved.