overheated

It would seem to me that oil analysis is unwarrented in this case as the root cause is very likely extreme overheating caused by lack of coolant. I would be camping on the desk of the manager of this Express Lube demanding that your engine be replaced.

Dullhook,
You are out of luck. The fundamental nature of RCFA is that from the damage done the initial point of origin can be determined. the seizure negates the possibility of determining that point because the overall damage will have masked the evidence. From the story your explination seems to be possible and even probably. But....the only way to PROVE is to repeat the exercise. The very nature of the failure you describe would preclude the meaningfull intrepretation of the lubricant analysis. For every "expert" you could bring to court to support your logic another could be brought to refute the logic.
Di I think the Express Lube is responsible, YES, but getting them to bellie up to the bar and buy a round might be hard.

I agree with BuckHntr, make sure the manager gets to knows you by your first name. Make sure you get to see him/her cringe when they see you coming.

regards.....