well enpony, I'll have to say, that "I'm bettin' with Bill"
As he has already said, the normally aspirated (VIN K) Series II 3800 engines of those years are essentially guaranteed to start sucking coolant internally sooner or later. And just as Bill says, Man you better hope that you don't have a "hydraulic (-or liquid) lock condition occur,,,, -I don't even want to talk about how bad that can be.
ANYWAY, if you haven't done so already, PLEASE read (AND HEED) the many threads that have already been posted on the subject, here on the Bonneville Club.
-and for what it'* worth, I came #$%@ close to totally loosing the engine on my wife'* '99, when it failed. -it sucked all the coolant into the oil, in a matter of a couple of minutes when the Lower Intake Manifold gaskets failed. I was already aware of the Upper Intake failing, and even had the replacement parts on order. But, we drove it a couple of days longer than we should have. I did end up having to replace the crankshaft bearings too, because coolant tends to cause instant death to engine bearings.
Sheesh, man, I would not be wasting any time on getting the problem defined.