I have one, right behind water pump, starting to weep a little on my 91 B2600i. Anyone ever have one come out? I noticed several parts houses have these rubber expansion plugs that expand when the bolt is tightened. Where I live I don't think I have to worry about the coolant freezing. I prefer replacing the plug with a similar metal type.

 

I haven't had one come out but you will want to replace it if it is leaking, you should be able to pick up a kit at your local parts house.

 

I have had one bust out on me about a week ago. I noticed a small amount of coolant around the plug about a week prior to it bursting out, and before i had a chance to fix it before it came out. In any event i am having difficulty finding a replacement part, i am considering purchasing a block heater in the hole, as i do live in a cold environment.