Did it in 5 mins to take it apart...The flat head looking screw in the middle of main cog is not flat..Its flat on the ends then starts to get deeper as you go in the middle..It's a bit like a slight V shape which makes putting the largest flat head screw driver in hard and slip easy. What I did was chocked it with some riggers leather glove between the clutch ring gear and main cog, got a screw driver thats roughly half the length of the screw, put it on the end of screw , got a hammer and gave it a light tap anti clockwise direction. This was enough to unscrew it over by finger pretty much. Then I took the star washer out that sits in ther, used a sprocket remover tool that came with my engine kit which is similar to a harmonic balancer removal tool. That pulled the main cog out easily. What you have to watch for is that on the shaft, there is a little key which holds the sprocket to stop it from slipping. Don't loose, if it comes off with the cog like mine did, just press it back onto the shaft with the semi circle bit into the shaft and the flat bit on top. Use a flat head if you need to press it down more.. The new seal can pretty much press in. I didn't have to remove the clutch cover/ring gear to get it on as it's not that much in the way..Installation is basically reversing the removing procedure..Also put a light dab of grease or 2 stroke oil on the new seal so it slips into position easily. Don't over grease it, just very lightly...