We have found William's word nemesis.
It's "ravioli." It has all the sounds that he has trouble with: R, V, and L.
It sounds like "wabb-ee-oo-wee" when he says it. He can get the "v" sound if he slows down and is careful, which improves it to "wavv-ee-oo-wee."
It's pretty cute, him enunciating as carefully as he can. He can get the "r" and "l" sounds better, too, if he takes the time, but he usually doesn't. I mean, why bother? Usually, he's only saying "ravioli" if we're having ravioli, so there's context working for him.
For the record, the school district's speech pathologist wasn't worried about these little articulation issues when she evaluated him earlier this spring through the gifted-and-talented program. She said it's pretty normal for a child his age, and she expects them to resolve as he gets older. I know that I had trouble with the "l" sound myself as a little girl; I used to call myself "JJ Warson." And I eventually outgrew it, so I'm not worried about William, either.
Maybe I'll just serve a lot of "wabb-ee-oo-wee" and let him practice...
P.S. I have a word nemesis, too. And I'm 35. My word nemesis is actually a phrase nemesis. It's "lawn mower." I can't seem to quite say "mower" right, unless I say it very slowly and exaggerate it. I say "lawn more." However, I think this may be a Southern thing. Sort of like "bold shrimp."