Chainsaw Repair

I have an early 600p, its muffler has two baffles bolted on where the exhaust leaves the can.  One of the pieces looks to be a screen holder and the other directs the flow.  This muffler appears a little different than some of the others that Ive seen in that it has an internal vertical divider/baffle running near the edges of the can about half way through the depth of flow.  The exhaust flows from the cylinder straight into the muffler then through holes in this vertical baffle, then up the front cover and out.  Its not that loud and flows well.   

After the initial supply of 600p build parts had been used, Echo advertised that they had redesigned the 600p engine for added fuel economy/torque.  This is also when we began to see the 590 and 620 versions.  Im sure there were changes made at this time to the cylinders and so on.   

My muffler appears internally different than the one in the video;
http://www.youtube.com/watch?v=pahXpy6Pbms