finally found some evidence of the old motor's demise (other than it being locked up, of course). i pulled the intake manifold last night, amongst other things. the intake valves all look fine, but the intake manifold itself is full of oil and metal.
not sure exactly how it made its way to the intake; my first guess would be AOS, but the AOS is fairly new & shows no signs of having been the source. after i get the carr running, i'll tear down the old motor & find out......