Final Update: It was definitely the two chamber coatings - The first coating next to the briar was like grey primer, the second one was the black carbonized coating. Maybe it was some kind of a glue to hold the pre-carbon coat on. I ended up sanding most of them off - about 80-90%. I washed the chamber; let it dry then re-coated it with a lightly flavored alcohol, let it dry. I then smoked a bowl of Country Squire Old Tobey and used the ash to re-coat the bowl. All smell and taste of diesel/petroleum seems gone now and the pipe smokes sweeter (for now). Thanks for the responses and suggestions; much appreciated ! ?