[mirwa]

Or, feel confident and remove the back, most older yamahas have a black binding strip around the perimeter, remove that binding and its very easy to seperate the back off

Fit new bracing, most guitar techs just use products from stewmac or similiar companies so get that for a cost of $30 I think, you can hold the bracing in place whilst drying with a kitchen table and some scrap pieces of dowel to put pressure on the braces for next to no cost

Steve