That's what I was thinking, but there was no signs of it even with the engine running. Come home from work today so see a second spot on the floor though that didn't tell a lot as its just run off the undertray. What was telling though was coolant sitting on top of the bottom radiator hose and on the tabs for the shroud, no marks of exactly where its come from but this leads me to either the cap or one of the vent hoses. The vent hose that leads to the valley was slightly more moist than the one to the overflow (which was bone dry) so those are my starting points. The hose has been a litte damaged on the outside from the hose clamp but no holes or cracks. I've cleaned up all the marks again now and will grab a cap on the way home from work and order a new hose. The GM part number for anyones refernce is 92158006 or Gates replacement is 02-1183. Although I'm not 100% sure either is the problem I'll be able to fit them on different days and see what works and I figure no harm in replacing a 20 year old hose, I guess this is the wonders of dailying a 20 year old car now. I adjusted the hose clamp on the hose too, so will be interesting if that makes a difference or if its still dropping coolant come tomorrow arvo.
I know this is pretty boring stuff, but hopefully explaining my methodology may help someone else one day having a similar issue.
Big mess on the bottom hose, obviously falled down from above somewhere
Similar story on the upper radiator shroud tab, indicating the drama is still upwards.