You will have to remove the old key and check if for damage, also check the slot in the hub for scoring or dents. If the key is damaged, replace it, it's a standard metric size. If the hub is damaged, you can take a fine file and clean up the slot at the end so the key will slip into it easily.

To reinstall, just slide the hub back on aimed as close to the key as you can get. Id should slide easily enough for you to fell when you touch the key and get it into the slot.

Make sure the three conical washers have the high side out, replace if you don't have them.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!