Oil/Coolant leaks

Here's my problem and from browsing these forums I'm sure not the only one with this issue. While driving down the hiway I hit a piece of metal that punctures my transmission coolant line. As the coolant is steaming out I notice that there seems to be oil in the mix. I limp the van into the closest dealer (30 km away). The dealer fixes the puncture then tells me that there is a problem with a bad gasket that has allowed oil and coolant to mix and they will fix this problem since it's covered under my powertrain warranty. The next day they call and say there is a problem. Once everything is back together they realize that a cylinder has been damaged to over-heating. They can fix it with a new motor ($3600 + 19 hours labour = $5000). My comment to them is that could this damaged cylinder have been caused prior to the puncture due to the leaking and mixing of oil and coolant caused by the bad gaskets? They get defensive and start backpedaling but essentially say no. I then tell them about a class action lawsuit in Ontario regarding the gasket issue. Their response is "innocent until proven guilty". This was encouraging. I have noticed many people having the same issue with the oil/coolant. I'll be calling my dealer (not where they vehicle is) and GM this morning but does anyone have suggestions on where to go with this? BTW, its a 2003 Montana with 75000 km on it. I have also seen references to Service Bulletins issued by GM regarding this problem. Where can i find the bulletins?