Your roof looks to be in great shape to me too though the seam thing is really unusual. If your having problems with the seam then I would just cover it in a wide swath with Eternabond tape and inspect around vents etc.
we did that in places where the decking seams mirrored through a bit behind the rubber. They did not leak but I was concerned about a limb, etc catching more on that slightly raised area.
I bought a 1990 motorhome last August and my roof has those seams in it as well. I am going to be puttin on a rubber roof as well. Liquid Roof and Rubber Roof are the same thing they are just marketed to different people and have a pretty significant price tag difference. I found a 5 gallon bucket up in Elkhart IN and since its close Ill be going back and getting it without all the delivery hassles. My roof overall is good but there is some cracking on the edges above the rain gutters. The people before didnt seem to take care of any part of it very well and have done some crazy self improvements that im having to tear out and redo.
Yeah I'm not so sure what the owner before me was thinking with some of the repairs. I just noticed that the siding on the cabover is popped out and instead of them fixing it correctly they just put sylicone over it and tried to keep it closed that way. Now I have to figure out how to get the trim off so I can push it back in and put the trim back on. I don't think the owner had any idea what he was doing and never tried to figure it out...