well, I checked the front of my '99 200se and I have the hole too...but it doesn't leak
I would honestly be more curious about why it's leaking; that would better answer if it's okay to plug
if that's leaking internally - how is oil getting there? when the engine was rebuilt, was it bored out? was there supposed to be a metal wall backing to it that is now removed?
if so, then plugging it is not the answer; you might need to re-sleeve it...
but who knows - better to figure out why it's leaking first