When I bought my '55 Plymouth, I changed the oil and it came out black and thick. I started it and idled it until it got hot, then I changed it again. I think I changed it about 6 times in the first few months, just to try and get as much gunk as possible out of the engine. The filter housing was hardened sludge up to the drain-back hole. Taking that off and digging what seemed like window putty out with a screwdriver made me feel better about the whole thing. Eventually, I replaced the feed and drain hard lines on the filter housing with braided AN lines so I could empty the filter when I do an oil change.