I picked up an older plywood flat back. It's borderline player/ project, but after spending a couple hours with it I think with relatively little work, it would be an OK player if called upon. Anyway, I've never owned a flat back before and when I looked at the soundpost, it is not sitting on the lower brace but rather a hole has been drilled through the brace for the soundpost to contact the back directly. I researched here and evidently it is supposed to be on the brace. There is no sign of any bulge on the back. At some point either the top or bottom has to come off due to some shoddy repairs (not sure which one is worse at this point). At that time the brace could be replaced if necessary (I assume that it is), but in the interim would it be wise to try and plug it with a piece of round spruce?