I put in new upper engine steady mount rubbers last night, and once back together I took it for a quick run to make sure everything settled. I noticed the car had a noticeable increase in power at higher revs, had me stumped, as all I thought I had done at the time was change an engine steady mount.

When I got back and lifted the bonnet to make sure the mount bolts were still tight, I noticed I had missed putting on the hose that runs from the clutch housing breather (Can filled with steel wool looking material) to the pipe which appear to run to the injection manifold assembly.

Why would having this hose disconnected increase power ? Or would it have no effect, and was I actually imagining it ?

And also, another question..
Why, after changing the rubber seals, would oil still continue to leak from the rocker cover bolts ? Pressure in engine too high ? I don't get it.

I wouldn't have thought you could notice the difference but basically that air tube would be unrestricted (no filter) straight through to the throttle body, so more air can be sucked in.