42 huh?! OK, I have to admit I have exactly the same problem with a pair, so I don't think I can help
I have a pair of percs given to me by the owner of a LFS. He picked them out for me on 104th Street and hand-carried them back on the plane. They came clean through qt-- I treated for internal parasites and started feeding them well. This was about two years ago.
They are in a stand-alone 20H (the pairs on either side of this pair are also in stand-alone 20H, were introduced later, and are both spawners). The female has gotten VERY swollen several times, I've even seen the ovipositor several times, but never any eggs. They are settled in a pot, eat well, aren't skittish at all, and the male cleans all the time.
I've never had a pair soooo close to spawning for so long without actually having a spawning event. I've tried blooms, large water changes, extra feedings, thoroughly cleaning everything. I think the next thing I'm going to try is moving them into a centrally-filtered broodstock system to see if that gets them going.
The only thing that would keep me from changing anything is that the fish just spawn when they are ready, and sometimes it takes a while. I have a pair of occ's that I bought in 2001. They paired up nicely and grew very large, but they only started spawning a few months ago
So basically I haven't added anything useful, but I'd also be interested to hear any thoughts
Matt