Way to many unknowns. You could very well guess you have found the problem and when it is back together it still leaks.
I am not a fan of guessing if every thing might be good. I personally like to see it.
As far as the O rings, I keep them on hand by buying 50 at a time. Send me an email to betterlife55 at yahoo dot com and we can figure out how to get some to you.
I, (myself would) remove all the sleeves and make the block look like the one in the picture and look for cracks in the lower O ring sealing area before starting to re assemble.