I'm not actually sure it's the opto....
I first noticed this during multiball; it would shoot out two balls at once, rather than one right after the other. I thought maybe the opto was misaligned, and wasn't seeing the lower ball. But if that were the case, it wouldn't shoot it up at all the rest of the game. So I watched it some more.
What seems to be the problem is that the ball sits there a bit too long before being shot up. I'm really not sure why. If it's one ball, you don't notice it because it does pop out okay. But with two, the first sits there a couple seconds and the next one rolls down onto it, and they both get shot up together. More of timing thing than an opto thing I think.
But I'm not sure why it's sitting there longer now. Maybe 2 seconds, definitely not more than three.
Any ideas?