So I've dealt with this damn thing just as many others have and I just started keeping a backup around. The petcock yet again stopped delivering fuel and as usual it's because the disc popped off diaphragm.

WELL I think I might have finally solved it; implementing the solution I wanted to previously which involved bracing the disc with a needle. So far I've got a few weeks, about 30 hours in 5 mph rush hour traffic, and around 800 miles without issues. So at the very least, it is working.

Here's what I did:

Equipment:
Quilting pins

Pliers
Phillips screw driver

Steps:
Get the petcock out of the bike.

Using the pliers, bend the tip of the pin so it has a bit of a curve.

Put the disc onto nub of the diaphragm so it is how it is supposed to be like in the picture.

Now push the pin in between the disc and nub so you are going into the diaphragm just below the nub where the disc sits in. Use the pic as a reference. You will want to wiggle the needle slowly and gently keeping it from piercing through before you get through the other side. This takes some dexterity and finger strength but you can use the pliers if you want.

Once through, clip the pin so it's long enough to brace the disc but not too long to interrupt anything.

Once it looks good, put it together and back in the bike and you're good to go!