Improper install

As you can see the piece is only held up by a flimsy piece of wood; which has warped over the last two years since install. The top,(I forgot to take a pic) has sunk resulting in ~1/4 " lippage at the seam & a noticable gap along the backplash. How should I fix this? The sink has no seam, so it may crack if I lift up the piece to shim. Should I try to replace the piece of wood with a strip of aluminum?