deep in the code / subscription_deleted hook

I am having trouble finding out where the payment hook 'subscription_deleted' is actually called from...top level. I want to alter the code to setup a similar hook, subscription_deleted_2 that also passes in the 'payment_id' field from the db.

I created another column on the payment table where I have a reference id I need to access when that subscription expires. I know the '$member' array passed in contains the payments...but I made another small additon to allow for multiple subscriptions of the same product, same billing period...so I really need to know EXACTLY which payment (as in payment_id) expired.

I realize I am making changes that are going to make it pretty difficult to upgrade...and probably not supported...but that's ok with me.

really great product, by the way.

thanks in advance!