EF 50/1.4 AF overshoots

I have a 50/1.4, bought about 6 years ago but not that extensively used. I've noticed some AF inaccuracy lately.

On my 5D2, I need to set a microadjustment value of -10 to get the average zeroed. However, when the initial lens position is in front of subject, the AF result is a little bit behind; when the initial lens position is behind the subject, the result is a little in front.

Something like this:

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In short, the AF always overshoots slightly. The error is clearly visible at F/1.4 and still discernible at F/2.2 or so.

I am wondering whether it's an indication that the lens is getting old or is it normal for 50/1.4 in general. Thanks.

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