My 400ex is burning oil now. I'm wondering what the best solution is. What would be the best oil additives to buy in order to seal the rings so my oil burning goes away or is reduced?

 

there is no "mechanic in a can" solution for worn rings. The best thing to do would be check compression, then add a teaspoon of engine oil into the spark plug hole and check compression again, if the reading comes up significanly, the rings are worn (seals better with the oil in the cylinder) if not, you have worn valve guides or valve seals. either way, you'd be taking the cam chain and cylinder head off, so doing a whole top end rebuild would be a good idea.

check compression with the choke off, throttle wide open, let the needle on the guage flick at least 4 times as a general rule. remember to disable the ignition.