thats like a regular sherlock holmes mystery. no metal filings where stuck to the drain plug magnet just that one lone chunk? Not sure why I am thinking this but.. easy possible check, I would remove your oil filter adaptor and have a look at it next to see if it has any damage in it. there is a little plate inside it held on by a tiny screw, it creates a bypass if the filter is clogged up so oil still flows. will affect pressure for sure if its broken off. there is a picture of it halfway down this page. http://www3.telus.net/68bird/engine_build2_3.htm
