Any suggestions on how to fix this gap? I was thinking of putting washers between the wood and hindge. The gap between the top of the leaf is 1/16 lower than the table.
Welcome to the forum, Mark.
Washers on the table top side might work. I would make a wooden shim the desired thickness and glue it into the hinge mortise to give the hinge full bearing and the screws full grabbing power on the leaf… Either that or cut the mortise deeper on the table top.
What kind of support does the leaf have?
I’d be inclined to drive some screws along the length of where they meet, like this:
Then adjust them so the top is completely level. Might have to be adjusted again as the wood on top compresses into the screws. Maybe if you put a metal plate where the screws meet that’s better, but I kind of like how the wood will deform around the screw a bit to better spread the load.