suck out the coolant from the cylinders and replace upper/lower intake manifold gaskets, mine was leaking coolant internally as well, luckily i found out before i hydro locked my motor
all Bonneville'* have shitty gaskets so im not surprised theres leaks
the reason for the gaskets to fail is due to dex-cool (anti-freeze) which eats through the crappy plastic gaskets. It took me 2 days to replace the gaskets with a buddy. but after you replace the gaskets CHANGE your oil lol.
BTW forgot to mention clean the upper/lower intake manifolds before you put in new gaskets
Pioneer DEH-2700 ~ PIAA Head Lights ~ Eye Lids ~ Tinted Tails
Gutted Air Box ~ Audi Style Headlights ~ Blue LED Interior
AC Delco Plugs & Wires ~ Xenon Angel Fog Lights