so to wrap this thread up, this is what I wound up doing and it turned out well.
I realized I really didn't want to start making new parts out of stainless, so I took a clsoewr look at how the old one was put together.
I noticed that originally the plexi does not go all the way thru the bracket, it stops at the top of the barrel on the 3 shoulder screws that hold the latch on. This leaves a pretty large gap between the plexi and the bottom of the bracket, about 1/2" or more. This area acts like a large crap trap, a reservoir for old sour coolant, rust, etc.
This is where I did it a little different from factory.Remove the latch and the 3 screws. Take a stiff scraper, like a putty knife but more rigid, and dig out all the old Silicone RTV and rust out of the slot in the bracket. It was pretty bad, there was heavy rust and even scale down there which I think came this way, I haven't seen my coolant do this on any of our machines. I washed it out with soap and water and then rinsed with Acetone. Clean the plexi with mild soap and water too, do NOT use Acetone on the plastic.
With everything clean, get a tube of Silicone in a caulk gun, I used Dow Corning 737 in a 10oz tube (pure Silione), fill the 1/4" wide slot in the bracket about 1/4" deep. Center it on the Window (has to be in the machine), and push it up on the Plexi. Use a dead blow and carefully tap it up until the plexi is as far as it can go down into the bracket. Securely temporarily with C-clamps to keep it from sagging and sliding down.
The screws will not go in now , so you will need a 25/64th" flat bottom drill. This last part is important, using a normal 120 deg included angle bit and drilling by hand can easily result in the drill binding and "grabbing" the plastic, which will crack it. Also, the hole needs to be clean with no counter-sink on the bottom like you would get with a normal drill point. I make my own flat bottom drill,really only takes about 5 minutes to do on a clean bench grinding wheel with good corners.
Blow out holes with compressed air and check fit of screws, make sure they go down all the way. Remove and a little more RTV to the threads of the screws and barrel of shoulder, add latch, and re-assemble. The plexi is now captured in the screws and completely engaged in the bracket, should be good for a very long time. Just need to decide if I do the other side now or wait for it to fall off first?