Take the back plate and carb off and drop it in a jar of fuel. That should loosen up the crud everywhere. You could probably even squirt some fuel up into the wrist pin area and let it soak upside down so the piston hold fuel like a little cup, thereby soaking the wrist pin. If you have a micro butane torch, pull the head off and heat the top of the piston, it will prob heat the wrist pin up enough to unstick the oil thats in it.
Put the whole engine in the oven, minus the carb at about 150-200 degrees for 10-15 minutes.