Control info is sent by the multi-conductor plug and socket connector assembly. There is very little inside to cause a problem with switches so the logical guess would be oxide buildup on the contacts from storage before shipment, like what happened with a lot of 18-105vr lenses in D90 kits. A light application of deoxidizer like Caig Laboratories D-5 would likely take care that minor and normal issue. Industries which depend on a lot of connectors and plugs, like broadcast, recording studios and pa sound companies live on the stuff, because all metallic connectors are subject to some oxidation, particularly if unused for a while.
That being said, I still have not had any problem with either of my 3rd party grips. But eventually I know I will need to treat the connectors, like on every piece of electronics I have. The D90 Zeikos has 75,000 shots on it and my D7000 with grip does not get as much usage, about 8,000 shots and has been flawless. The majority of shots are in vertical orientation with both cameras so at least I know the AF-L/AE-L button(AF-On) and the shutter release can take it.
Stan
St Petersburg Russia

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