It seems this split gives me an oil leak..affect power?

If your talking about the main pipe in view. Thats part of the PCV system which recircs excess air pressure back into the inlet from the engine.
a few things to mention.

1. the pcv system makes the oil vapours OZONE friendly by placing them back through your engine, which is why you have a slight leak below.
2. alot of people just block off the pcv system, i have recently done mine, which means no leaks, less oil going back into my engine which means more "good" air not mixed with oil vapours.

O and 3. if the pcv system is leaking, it means you are loosing boost pressure, which means you will be down on power, only slightly i imagine but when its blocked or fixed you will notice it.

I used the forge blanking plate myself, and noticed and instant better drive. Its only about £70 and gives your boost tap options in future for a boost guage or meth kit etc..