I was having this same problem and replaced the tumbler. When I got it all back together it locked up again, and it took me hours of wiggling to get the key to turn again. I bought the $80 steering lock from Phil, and it has worked well ever since. If you can get your ignition to turn you do not need to grind the pin. If your lock is stuck try wiggling vibrations and anything else you can think of before you resort to grinding the pin. The lock assembly is fairly easy to replace. You can follow the dieselgiant guide, but if you can turn the key to position 1 you can just press the pin rather than grind it down.

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine