Welcome to- The Fountain Pen Community!

Good news/bad news time.

1) Be very grateful you got the section out. I've run across dozens of these over the years that would NOT break loose despite my best curses & scariest threats of harm...lol.

2) The buttons are not designed to come out, they were set in place and the button 'flared' on the inside to keep it in place. You'll need hemostats or pliers to wrench it out. If the pointed/tapered end of the dead bar are still in the inside of the button, you'll have to get those out before you reinstall the new one. A long drill bit size 1/8"(? or there about) should ream it out properly.

A j bar isnt really that great to fashion a button filler bar. The rib/ridge down the center is designed to keep the bar rigid & to prevent it from flexing. If you have some beater wearever button fillers around those are a dead on fit if memory serves.

Also yank that crappy steel nib & drop in a 14K organ donor. Any equally sized gold nib should drop right in with little to no problem.

Progress made! I happened to have a piece of junk, no-name button filler in a pile of parts. So I got my pliers and yanked at its button and the whole assembly including part of the barrel came off. I'm glad I didn't attempt this on the Waltham lest the same thing happen. But the pressure bar was intact and corrosion free. I'm fairly certain that with the right amount of care, I can actually insert the bar without removing the Waltham button. I tested it minus the sac and it seems to be work. So next test is with the sac :) Thanks Dennis!