I've been chasing and chasing a shower stall leak in a shower stall installed about 15 years ago (fiberglass, one-piece). First I found a leak in the floor drain flange. Had to chisel it open from the top given the hardened "sealant" previously used. Replaced top and bottom pieces, followed proper order of gaskets and sealed top flange with plumber's putty.

Next found leak in P-joint connection where ring tightens, fixed that. Next found slight leak in 2 inch pvc connection. Got that to stop with cleaning and re-swabbing with PVC glue (nearly impossible place to try to rip out and replace without lots of dry-wall/frame tear-out).

Also, sealed up the faucet wall plate much better.

But I still have a slight leak. I'll do better inspection, but I am about sure it is coming again from the floor drain. Only have a leak when I shower. Not when I just run water, or my small children use the shower. I'm about 160lbs.

I do not believe the shower floor was well reinforced (packed). However, I really cannot see any noticeable deflection.

Is it advised that I try to reinforce the shower floor from underneath (I have some tight access through a hole in the ceiling below) even though deflection is not really noticeable? Is there a practical way to do this with very limited access from underneath?

Is there a product to use better than plumber's putty to seal that drain flange that will stay in place well while the flange is screwed down, and will subsequently better handle a little possible floor movement?. and will let go if I need to again remove the flange.

Only have a leak when I shower. Not when I just run water, or my small children use the shower. I'm about 160lbs.
I do not believe the shower floor was well reinforced (packed). However, I really cannot see any noticeable deflection.
Sounds like the shower floor gives just enough to break the putty seal on the drain lip.

Is there a product to use better than plumber's putty to seal that drain flange that will stay in place well while the flange is screwed down, and will subsequently better handle a little possible floor movement?. and will let go if I need to again remove the flange.
You will have to remoive the flange to reseal it.
Try removing the putty and sealing with a more flexible sealant such as Silicon Jel.

Is it advised that I try to reinforce the shower floor from underneath Every plastic shower floor should be bedded in and reinforced to prevent the drain seal from rupturing. Good luck, Tom

Speedball- Thank you very much for the quick response. I'll pull the flange and use silicon instead of the plumbers putty. I also notice the local Menard's sells a foam-like ring gasket labeled as a substitute for plumber's putty on this drain flange. Are you familiar with this product and would it make sense to give it a try?

Also, I noticed you once suggested to another help-request that you could provide methods to bed an already installed shower from access underneath to strengthen the shower floor. Could you provide this advice. I'm thinking of using expanding foam, but am concerned that will bind up the drain assembly/piping should I ever need to get them apart.