Rollei 6006 - Magazine / Insert question

Picked up a used 6006 system, 80, 150, prism finder, extension tubes, decent battery and case. Thrilled to find one in this kind of shape at a reasonable price. Used a 6002 extensively through the 80s and always felt it was a better camera over the hasselblad c/m, own both now.
My problem is with the magazine or insert, winds up fine to the first frame, film advances on every shutter release however doesn't advance fully, some over lap of photos once I develop the roll, two or three frames overlapped or half the roll. (120 film Tmax 400). Winds the complete film after shot 12 is fired.
I have since ordered a second back on ebay, should correct the problem.
Noticed a minor cracks on the inserts, both sides, could this be the cause of the film advance problem? flex in the insert?
Any other things I should look at to resolve problem and give me two reliable magazines?
Thanks,

This is probably not your problem but make sure you have the correct film insert. The older SLX style is different from the 6008 style.

Film inserts of the Rolleiflex SLX (which may be recognized by interior icons and indices) should not be used because they may jam when they are removed.--Rolleiflex 6008i Manual

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OK, thanks. Believe it is the correct insert, does not have any icons on film alignment marks on the interior. You don't believe the stress cracks cold be the problem then.