Where might I find/identify said breather or vent? Is there a good manual on this motor? The best I have has been cobbled together from Defender 90 docs...

I have a 90s Rover 4.0 in my MGB, and oil is pooling up on the top of the engine (below the air intake). I've...never seen this before! It pools up after every drive. Where could this be coming from? The valve covers are seeping a bit, but they're dry where the oil would be dripping down onto...