The best course of action to future proof is by removing the old cast iron flange. This youtube shows one way to do it. If it is a process you are not comfortable with, maybe let a plumber handle this one.

 

In a facility where I managed the trades, there were over 8,000 closet flanges- all cast iron. The plumbers' favorite repair was a stainless steel ring that drops over the defective cast iron flange and then is screwed to the floor (concrete in this case, but works on wood floors, too). A similar one is pictured below.

These toilets got abused, beat up and abused some more. The stainless steel rings held up fine. They also survived repeated floor floodings with chlorine. (Not so much the concrete screws, but the flanges didn't rust.)

There are many brands. The Oatey one just happened to be one with a photo.

Hope this product helps speed the job along.
Paul

 

Oatey® Cast Iron Closet Flange Replacement | Oatey

Oatey® 4 in. Replacement Closet Flange installs easily without tearing up your flooring or caulking piping. It fits inside of 4 in. cast iron or Schedule 40 DWV piping (sold separately). Its rubber compression gasket allows the flange to be used on many types of cast iron piping. Oatey products...

www.oatey.com

The existing flange should pry right off.

 

With the house being 50 years old, the flange very well might be attached by a No-Hub type connector. (Can't tell from the photos) Prying it off could open a proverbial can of worms unless access to the coupling from below (such as from the basement) is available.

If there is a No Hub and it's accessible from below, then the job of replacing the flange is quick and simple.

Paul

 

I appreciate all the suggestions. I watched the This Old House video and have ordered the Oatey flange replacement (that tightens into the drain pipe) and also one of the steel ring replacements to see which will work best. I am still unclear why I would need to remove old flange if I use the Oatey flange repair. Should I aim to have the flange sit on the finished floor if I use the Oatey flange (insert) repair?

 

Hi Maplest25,
With the repair part that inserts into the existing pipe, height is the question. You'll need to measure how tall from finished floor to top of new flange. Next measure the depth of the skirt around the base of the toilet bowl. Compare the measurements. There should be at least 1/8" clearance for a wax ring.

If the depth of the skirt is too shallow, then you face removing the existing flange for an insert type flange repair. A steel ring, such as shown in #3 will not require the existing flange to be removed. It "caps" the old flange, adding less than 1/8" thickness.

Hope this helps explain!
Paul

 

Again want to thank everyone for their help and particularly thank consideritdone.na for the this old house video as I purchased the Oatey 43538 ABS Cast Iron Flange Replacement, 4-Inch and installed it. I also have learned why my toilet leaked in the first place. I have an American Standard Cadet 3 toilet. When I removed the toilet it there was no wax mess on the bottom of toilet. I spent quite a while chatting with the Microsoft co-pilot AI about this. Turns out the toilet horn is only 1/2 inch high. The co-pilot was great in helping me figure the correct placement height of the flange. I had to set it at 1/4 inch above the finished floor. This allowed 1/4 inch of the toilet horn to enter the flange and allowed 1/4 inch of wax compression. I unfortunately ran into a problem with the tank to toilet bolt hardware that leaked when I began filling my tank after installing toilet and it allowed water underneath my toilet and onto the bamboo flooring. So, I had to remove the toilet to dry the flooring. The good news is that the wax had clearly compressed onto the flange and bottom of toilet so I know the flange is at the right height now. I don't know if my toilet was defective in having such a short toilet horn. If they were always made that way, then they should let people know that the flange has to sit 1/4" above floor in order to sit the toilet properly. Any lower doesn't allow the horn to enter the pipe or the wax to compress and any higher doesn't allow room for toilet to sit properly on the floor nor allow room for wax to compress.

 

Glad to hear that your repair was successful!
Your choice of repair flange is good because it can be easily replaced. (Plastic ring flanges break when a toilet is bashed into or leaned upon when not supported properly.).)

In the future if you ever encounter the no wax seal situation due to a low flange or a short horn; on the market are what are called "Extended Horn Wax Rings". There are also thick wax rings and synthetic & compliant no-wax rings. Any of those can solve the too low flange problem quickly for you. Plus, flange stackers exist. (I advise against these for residential.)

And if you encounter a flange which is too high, there are toilet bases on the market to compensate. Not pretty, but work.

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On - Below - Above....???
As far as the Flange On The Floor versus Flange Below the Floor- this debate has been going on for decades. When I apprenticed, all flanges were brass or cast iron. Brass rings were rather thin, thus underside of flange was on finished floor. Cast Iron rings were thicker. We used top of flange 1/8" above finished floor.

When PVC and ABS showed up with the thick rings, the debate started. We ended up using top of flange flush with or up to 1/8" above finished floor. Never below.

But there is No absolute correct way. It depends on the fixture:
In my home, one of the toilets will not work with a PVC or ABS flange above the floor.The skirt is too short. The flange has to be stamped steel and nearly flush with finished floor. Also in my home are two toilets with a tall skirt, requiring a stacked wax ring or similar. (All are American Standard, made in Aisa. So much for "standard" & for "American".)
And we have an ancient LaMosa back fill tank that has a perfectly sized horn & skirt.

I should have plumbed for wall mount instead...

 

I've used this one twice now with easy results. A couple dollars more than a cheapo wax ring.

https://www.danco.com/product/perfect-seal-toilet-wax-ring/