I've heard of doing this using stuff ranging from ATF to Mineral Spirits Fortunately the old VW engines were the next-best thing to a stone axe, but less complicated and more forgiving of mistreatment.

If your oil passages were plugged, you would set a new record in oil-change intervals measured on a series of calendary pages and your diesel would probably be overheating big-time!

Just change the oil.

BCingU, Jim