The tumbler is a design flaw (or planned obsolescence from Huf). It dies somewhere around 100-130K miles. It's also well documented here, if you want to try the DIY, but you should do it before the tumbler really does stick and won't turn - that's significantly more costly because you can't line up the slot to remove the tumbler. So, if it's ca. $200 including part, then I'd be OK getting it done.

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Prost!