Ok, after reading over and over all the people who have had issues, no one seemed to nail the problem. But I think I did.

when I removed the pump from the housing, I did take it apart to inspect it. I left the o-ring and plastic piece in the filter and sandwiched it back together. Everytime I took it apart it looked the same, the o-ring was at a bit of an angle when I pulled it out. Figured simply how it got pulled on no biggie. I went to the junk yard to get a pump holder to have one I could mess with, and carefully examine how factory assembled. Looked the same as mine.

But the difference. When I removed the filter side from the mount side, it was HARD to get out, mine, EASY. hmmm, why? So this time I put the o-ring and plastic piece on the mount side (the top part with the connector and output line) and then installed. Now to take apart it was HARD to do. Ah ha.... It put the o-ring in a different place in the filter.

So far 2 days now, no problems.

I can say the 1999 RX300 has the same fuel pump mount and holder, but a smaller fuel pressure regulator and siphon jet (5/16" hose instead of 3/8"), so you can use it and just change over to the GS400 parts. And a 2000's Corolla also is the same, but has no siphon jet on the regulator, so it would work too. Just change to GS400 (or 300 or 430) regulator parts. The outlet fitting is the same on all.

We glanced as early 2000 or so Camry, same parts in the fuel pump mount. So feel free to grab some spares! It gets you the unobtainium parts you can't get from anywhere! Grab spares. I have a few now, not taking that chance again.

 

Long term update installing the pump like I did in post #16 is the solution to this problem.

Be a couple k miles now, no issues.