I had one that was so seized I ended up pulling riser and manifold and taking to shop to get it out.
Thankfully its easy and fairly cheap to remove / replace. I am using all new hardware to be safe and give me piece of mind (new gasket + bolts for both riser and manifold).
Its hard for me to let things alone that I know are messed up and can be taken care of with a little time and effort.
I read that about a quart of water will come out of the manifold plug. On removing mine, that seems like an accurate figure. Water sitting in a cast iron manifold can't be good and will definately rust.
I agree that new brass plugs every season might be a good idea. They are less than $5 each.
Last edited by Lumbergh; 10-26-2011 at 06:29 PM.