It appears that we've got quite the running theme going on in this forum...
I, uh, don't really know what to say, as I've been here before. I mean, I'm Importing it into Blender, and I'm able to do the non-manifold check from there, but after I've got that selected, whether I try to fill or delete things from there, it just seems like I'm doing things wrong. I'm certain the scale isn't how I want it, but that's because that's the last thing I adjust, after everything's manifold and ready for uploading.
I have a number of older models that I'd like to try uploading, but they essentially get the same issue, so if you'd like to talk about the process, I'd really appreciate it so I wouldn't have to ask for help every time I have something new.
Thanks in advance.