I discovered a leak in my shower pan. By selectively flooding portions of the shower pan, I narrowed the leak to the drain area. Due to the fact that there is no replacement wall/curb tile, I asked the contractor (repairing under warranty) to attempt a spot repair of the liner just around the drain. Approximately 12x12 inches of tile/mortar were removed. Then a new piece of Oatey PVC liner was adhered to the original liner. Then we leak tested, and it failed.

Now the contractor wants to try a more exotic solution, and I am concerned about the long term viability of the solution. His suggestion is to cover the exposed shower pan liner with one of:
1. 3M 80 Rubber & Vinyl Spray Adhesive

2. Amazing Goop 5400040 Coat-It Waterproof Epoxy Sealer

3. Rust-Oleum LeakSeal Flexible Rubber Coating

4. Flex Seal

5. FireShield® EPDM Elastomeric Roofing Membrane (water-based acrylic rubber liquid that cures to form a seamless rubber membrane)

Has anyone on the forum tried any of these in this situation and can vouch for the long term effectiveness? I feel comfortable that the leak test will show if the seal is successful at install time, but I don't know about how long the product will last. I also have some concern that the installation of the patch has created a "ridge" the water will not get past, negating the purpose of the pre-slope. Adding additional materials just heightens my concerns about this. As background, in initial conversations about the patch, the contractor said it would be installed like a shingle- at the overlap, the new piece placed under the original lining- but when the plumber actually applied the patch, he put it on top because he said it was not possible to place it underneath the original lining.

Does anyone on the forum know what codes or professional bodies or technical manuals might apply to this situation? Given that the work is being done under warranty, I don't have the (free) option to simply work with a different contractor. The contractor has taken the position that I have to convince him this is a bad solution. As a non-professional in the field, this is a difficult position to be in. How do I find information to prove if this is okay, or not okay?