I have a 1989 240 wagon. I want to change the lub in the rear end. What lub is everyone using? Has anyone tried an synthetic gear oil?

 

Well, you most likely have a run of the mill 1030 axle. If you want to know for sure, you could crawl under the car with a can of brake cleaner and a rag. There is a tag on the drivers side rear facing axle tube. Carb cleaner will wipe the label blank but brake cleaner will remove the goo without the ink. Should be a 3.73 ratio as those are most common. Given your car probably has a good 200k on it by now and it is an open rear end (not limited slip) any 85W-90 gear oil will work nicely.