Would these be effected by loose chips? Dirty mechanisms?

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Try pressing those keys about 40-50 times in a row, with a bit more pressure than you usually would. It is quite common (as in, I've had this, and so have others) for a keyboard that's been out of use for awhile to get key switches that are no longer making good electrical contact. Giving them exercise is the simplest solution, and should always be attempted first.