Normal on most older diesels. Just change oil and filter every three thousand miles and wear protective gloves as the old oil almost stains the skin. In fact if it was not totally black after a short run your engine is probably fairly clean inside.
Look at the upside as well. You can usually identify the oil level with only one wipedown of the oil dipstick. Some of our gas cars I have to do it a few times and still not positive if it's accurate. I really find it harder with off white plastic dipsticks on some of them and clean oil.