Replacement for Mansfield Toilet model 48 Chrome Push Button Trip Lever

My house has Mansfield one-piece model 700 toilets – which are quite nice, but have a rather unusual push button flush mechanism. The chromed brass push button and trip lever are model 48, which is no longer made and out of stock everywhere. You can get push buttons that look just like them, and I got “Rrina 2Pcs Push Button Toilet Flush Lever Handle, Universal Side Mount Toilet Trip Lever Tank Flush Lever” from Amazon for $12. There are two catches. The first issue is that the button is chromed plastic rather than brass, which really doesn't cause any problems. Unfortunately, the second issue is that the trip lever mechanism doesn't fit the toilet. Why doesn't it fit? Well, the tank is double-walled and the hole in the inner wall isn't large enough to let the lever mount far enough back to engage when the button is pressed. There's also the detail that the locking nut that comes with the Rrina has wings to help hand tighten, but those prevent you from putting a socket wrench head around it, which fits in the space between the tank walls way better than your hand does.

Here's my solution. Buy the Rrina chromed-plastic button and 3D-print custom mounting and trip lever parts. I strongly suspect similar-looking kits have compatible chromed parts. Then 3D print, using PLA or your favorite material, the following simple parts: locking nut, washer, holder, and thrower arm. You'll also need a ¼-20 bolt and nut. To assemble:

1. Remove the original button assembly. If yours is like mine, all the metal parts are badly corroded and this step will be challenging. NOTE THAT THE THREAD IS REVERSED, SO IT IS TURNED RIGHT (CLOCKWISE) TO LOOSEN. This reversed thread seems to be standard for the buttons, as both the original and replacement part have it. After much pain, I found that a few squirts of Free All Deep Penetrating Oil Rust Remover on the parts inside the tank worked like magic to free it up to a level where a socket wrench could do the work. If you're not so lucky, the original is a huge pain to remove because it is made of very solid metal and you can't get enough access to the shaft to easily cut it with a saw.
2. Put the new chromed button in from the tank outside and secure it against the inside of the tank's outer wall using the locking nut. A 13/16" socket can be used to tighten the printed locking nut but DO NOT OVERTIGHTEN. It should be just tight enough that the button will not easily spin on the outside of the tank.
3. Assemble the holder and thrower arm using the ¼-20 bolt and nut. You don't need to make it too tight; the bolt is simply used as a low-friction pivot for the arm.
4. Put the washer on the threaded part of the chromed button inside the tank. There wasn't any washer in the original version, but this oversize washer covers the larger hole in the inner tank wall, which makes things a bit neater as well as providing some flex tensioning for the next part.
5. Screw the holder and thrower arm assembly on after the washer. Tighten it only enough to stay in position with the pivot and bolt on top.
6. Adjust and connect the pull chain to one of the holes in the thrower arm. I used the last hole, but you have options.

You're done. Remember that, just like the original button, this mechanism needs to be held in for a second or two to do a complete flush. I don't notice the difference in the weight of the button due to it being chromed plastic rather than metal… but I do notice that the button doesn't have any friction, whereas the brass inside the original must have corroded pretty badly. The all-plastic replacement shouldn't have that problem. Better still, if/when the chromed plastic one fails, it can be removed much more easily, in the worst case by cutting or breaking the chromed plastic.

The photos work backward from the completed repair…