Checking out my f7 and found mag cylinder and piston scuffed. i think i had a cold seizeure a few weeks ago and thats what did it. YOU NEED TO LET THESE THINGS WARM UP BEFORE U HAMMER ON THEM. right now though the sled still runs strong and if there is any power loss it is not noticeable whats the deal with pistons and cylinders? how long are they backordered for?