enter
nvram set 5_x_PPPoEMTU="1400 default-asyncmap debug"
then press Refresh
After that enter
nvram commit
press Refresh
You will need to reboot router (power off/power on) and it should connect in the correct mode. Also in IP config in the MTU field you should see the "1400 default-asyncmap debug" value
now all things including internet are working on the router
but that is not all for aol
you need to change the MTU setting on your local client to 1372 to get your browser working correctly