Bosch KGN39V00GB/01

This FF was was frozen solid in the freezer compartment. I cleared the ice and raplaced the TOC as it was blown. Ive since read about the Mod for this unit. Im now wondering if i may get a call back on this as there is a slim chance (as i thought at the time) that i blew the TOC myself while defrosting it as i didnt know where it was located. Everything else checked out ok. My questions are, (1) Does this need the Mod kit its dated FD8608? (2) What actually causes them to ice up because if it were just a design fault would it not do it from new and not 3 years down the line? (3) Are bosch repairing them free of charge out of warranty?

Thanks

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