American Standard flush valve kit

[Elektrishun]

Hello
First post. I have an American Standard 6.0 L Champion Williamsburg 2 piece toilet purchased in 2008. Today I tried to flush the toilet and the lever gave way, no resistance, and no flush. I lifted the tank lid and could see the center plastic rod of the flush valve pulled right out the top. It was all intact, nothing appeared broken.
My assumption is the O-ring is worn enough that it can pull through especially when sitting in a full tank of water.
The flush valve is considered the old style with nut on top.
Does it sound like a simple matter of a flush valve repair kit? Replace the O-ring and gasket and good to go?
As well, I have watched a few videos of people replacing the O-ring and gasket. They unscrew the top nut and let the plastic rod drop down. If I did that the plastic rod would fall all the way through, nothing stopping it. I don't see any signs of something missing or broken. Just a different style or is there bigger issues with this flush valve?
I can still replace everything. I have already removed the existing O-ring and gasket, but I have to be careful not to let go of the rod when the nut is off.
Any help would be greatly appreciated.

 

[Elektrishun]

Update

Figured out the problem. The bottom half of the "flapper" where the plastic rod runs through has signs of plastic missing. I am assuming this is why the rod was able to pull out the top easily and why it would've fallen out the bottom if I let it go after unscrewing the top nut. The plastic must have become brittle and failed over time.

Since a new flush valve wasn't attainable off the shelf I decided to fix the old one. To get the toilet working I did the following:

- went to go my local Home Depot (Canada) and bought a replacement seal. Chose the MOEN Flush Valve Seal for American Standard/ Kohler Replacement Model # M5327. Does not come with the O-ring for the top nut but has a much superior looking seal vs the Korky brand seal that does come with the O-ring (the Korky brand large seal looked inferior because it had rough cut edges, like it came out of a cheap 3D printer).

- at the same Home Depot I picked-up the Moen Pro-Fix O-ring Kit M3762 for a Wallaceburg 3244 faucet. In the kit there's about 4 O-rings that are the exact same size as the original for the American Standard flush valve.

- now I had to fix the missing plastic. Otherwise when the flapper lifts up the bottom half wouldn't be attached and the flush is very weak. Easy - drilled a small hole on the outer edge of the bottom half of the flapper, through the seal, and upper half of the flapper. Made a small rubber washer from a larger rubber washer to receive a small stainless steel screw (#0 Robertson head SS screw that is 1/2" in length). Screwed the top of the flapper and bottom together. The washer under the screw head prevents water from seeping past (likely unnecessary since the screw passes through the seal sandwiched in between the two halves).

Does it work? As good as it did before which has always been exceptional! Best toilet I ever bought. Can't remember it ever being clogged since the day I bought it sometime back in 2008. Remember the American Standard Champion ad of the toilet with the bowl filled with golf balls? That's the one I have

I included an image of the flush valve so that people less familiar with this product will have a better idea of what I am talking about. The yellow arrow is pointing to where the plastic broke (not sure what the original looked like before it broke). The red line roughly shows where I drilled the hole and added the SS screw.