I know this is an old post, but it should help anyone who's experiencing issues with a leaky solid valve. I was having the same issues as this post.
I finally contacted S&B, explained the situation, and they shipped a new
Solid Valve Housing
Put it on, and it solved the issue! I guess the base of the housing wasn't flat enough to make a good seal?
Not sure, but anyone experiencing issues with a leaky solid valve should contact S&B for a new Solid Valve Housing.
Edit:
Where exactly is the leak coming from? Check out this post, it might solve your issue.