OK as usual, the act of finally posting my problem triggers something in my brain that helps me find the solution. The problem is the PayPal form. For some reason it is not recognized as a "form" by WA and therefore even though it IS a form and is POSTing it doesnt trigger the email.
I figured it out by adding a dummy form with nothing but a button to the page, which triggered the email just fine.
I therefore changed the email trigger to "before page loads" which isnt exactly what I had in mind... because I wanted it AFTER the person committed to buy... but at least I am a step further along.
Maybe someone knows a way around this or has encountered it before?