ok - I found a thread on "another Volvo site", and it had a long thread regarding batteries leaking in what is referred to as the "siren module". It is located as you stated, under the fender liner of the front passenger's wheel, forward of the wheel.

Evidently, there is another component of the alarm system, the upper control module, and I don't know where that resides.

From what I read, some people have successfully repaired the module (I should be able to, as mine is itermittent and I'm capable of circuit repairs), and resetting the system appears to not require a dealer. There is a 3x lock/unlock sequence that appears to do it.

I'll dive in, and report the results.
Thanks again for the tip - I didn't see the hits elsewhere when I posted this.
Don