[Lynn Eades]

If that doesn't work, try pouring a little diesel in on top of the pistons, and set fire to it. You will need to put in a bit of rag to act as a wick.(to get the diesel to burn) You might have to go through the process a couple of times.
What it does is warms up the various components a little bit. They all expand at different rates, and make the bits move slightly, relative to each other. Give it another clean on top of each piston, and give it another oil. try moving it again