oil is coming out of the rectangle plate behind the exhaust

nigel, April 2013

You've tipped the mower on that particular side and have caused excess oil to migrate into the crankcase breather. Start the mower and with gravity and engine heat your problem will disappear.

pleasant, April 2013

I would guess that the plate gets sealed up with a gasket and that the gasket has failed - that or the securing bolts need to be tightened up - possibly both gasket & bolts.

People with the same make & model as you have may be able to offer more realistic advice.

Good luck...

Peccavi, April 2013