When I replaced the one on my SD, I just poked the release pin with something (a coat hanger I think...) through the gap between the column and the dash near the opening for the tumbler.

Have you removed the circular collar that clamps the base of the lock housing, where it meets the steering column? If not, you'll need to, as it covers the lock pin that we are talking about.

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-Josh
Testing the cheap Mercedes axiom, one bolt at a time...