Find the DYI on this website on your tumblers and buy a new one from the dealership. I paid 80 bucks for the tumblers and four new keys. It's not worth the risk of locking those tumblers up and having to drill them out. It sounds so easy but drilling may ruin the switch.

My first encounter with a frozen tumbler cost me two days trying to get the tumblers loose so as to remove them then two days drilling to get them unlocked. I also had to buy a set of tumblers and an ignition switch which I destroyed with the drill bits.

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84 300SD
85 380SE
83 528e
95 318ic