I am in the process of remodeling my bathroom. My existing tub is in good condition with the exception that there is a small amount of rust around the drain flange. This is not hard water surface rust, it is into the cast iron. I am replacing all of the existing plumbing including drains. If I can come up with a new drain that has an oversized flange outer diameter, it would cover this rust area and I could avoid replacing the entire tub. Does anyone have any leads. I am a newby to this forum. Any help would be greatly appreciated.