I think this is unrelated to your build Whiskey. Just FYI, why I'm not a fan of goop even as a gasket.
The following is a bracket, liner, glass, frame system. Same deal is used for skimmers and bottom drains. Virtually every pond builder puts some goop between the liner and glass. And it certainly can plug very tiny gaps. The EPDM also does compress so isn't a bad gasket. This system works very well, has worked on countless ponds and I don't read about many problems.
What concerns me is what could happen over time. The bracket, liner and glass will all expand and contract at different rates. The bolts put different pressure points on the bracket. There is a potential imo for the bracket to pucker some place.
The actual pucker would be much less of course, and the compression of the EPDM is probably enough to fill any gap in virtually all cases. But goop, not being able to expand, does nothing to help. Goops depend on bonding to surfaces.
If instead a neoprene gasket is installed between the liner and glass, being compressed, the gap would allow it to expand and fill the gap.
Neoprene gaskets are super cheap and easy to install, regular neoprene, or PVC, foam weather stripping tape from the hardware store. for about $3. It's cheap insurance in my book.