Artist nightmare

I'm in my studio, working on a painting that's close to being finished. It's on a large, horizontally oriented Ampersand panel. [Gesso-covered Masonite mounted flush with a two-inch-deep birch plywood framework.] I don't know what the image is, but on a large expanse of what seems to be flesh I notice an odd, slightly darkened round-ish patch. Small, about the size of the end of a pencil eraser. The surface of the painting is wet. I put my fingertip on the discolored place and rub slightly, and the paint - and gesso - come away, leaving just the bare Masonite. I'm not particularly alarmed; the small section that came away is just fairly flat color, and should be not too difficult to match. I tilt the panel back, catching the light differently, to examine the surface for any irregularities I might not have noticed previously. What looks like a taped join - under the paint, under the gesso - going vertically and through the point where I found the problem is fairly obvious in the otherwise perfectly flat surface of the Masonite. I tilt the painting back down and now I notice another small section of paint loss about four inches to the right of the first, and the apparent join has become horizontal rather than vertical; both areas of paint loss are along that line. I turn the large panel around to the back side and see that, indeed, the surface is actually in two pieces, taped together with what looks like a few layers of that wide brown paper tape they used to seal boxes for shipping. The top edge of the tape has mostly come away from the surface of the panel, the edges curling out and then back toward it. I turn the panel back around to the front, only to see that the butted seam has shifted now, making about an eighth of an inch separation - the edges still in contact - most of the way across the panel. Along the length of the dislocated seam the paint surface has lifted slightly from the two edges of the Masonite, stretching and in some places torn. I'm still more annoyed than shocked. And pragmatic, thinking first that I should just replace the brown paper tape. Then deciding it will be much better to put the panel on its face and glue a piece of wood to the back of the seam, doing this all on a nice flat surface to ensure that the front of the panel will be as smooth as possible when the repair is finished. Then I'll repaint the damaged parts of the painting. I can do this. I'll fix this.