I am having trouble with my snowmobile bogging down. It starts and runs fine for the first few minutes. Once it warms up, I have trouble with it bogging down around 4000-4500 rpm. I can feather it to get it above 5000 rpm and it flys. I've tried cleaning the carbs twice and replaced all fuel lines and spark plugs and new gas. I've checked compression when cold and measures 130-135 per cylinder. I also blocked all ports and pressurized the engine to 8-10lbs. and noticed a small leak(foaming soap) around the crank seal and bigger leak around the exhaust gaskets. A parts salesmen is convinced I need to replace the crank seals. Does the symptoms sound right for a crank seal leaking? Any advise on changing the seals? This is my first time tearing an engine down.