my oscars are clearing the gravel, locking lips and other signs of possible breeding but nothing ever happens, any ideas?

Welcome to the world of the Oscar fish The majority of oscars will do this, even if they are alone in the tank. It's difficult to say really, we are looking at behaviour of captive fish, they may well behave very differently in the wild. If you think about it, in an aquarium, most of the time they are forced to live with each other, this wouldn't happen in the wild.

breeding can only manifest once oscar laid eggs but not an assurance
you can propagate them. there are times two female will lay eggs too
but won't hatch due to the absence of fertilization....