This is a really good question to which I don't have the answer.
A few days or a week or two might not make much difference but once you start getting into months or continually over the course of years I'd like to know myself.
Generally the weights are usually glued into place on most keyboards and there was an issue with older Kurzweil PC3 weights dropping off because of defective glue over a decade ago.
Honestly I'd have to say it would seem to depend on the manufacturer and the model and the general build quality of the unit.
I don't really think that orientation would have that much to do with it.
Normally weights are suspended vertically beneath the keys by glue to begin with.
Rotating the keyboard might create an additional shear force which could conceivably cause the weights to fail a little quicker.
But ultimately it boils down to individual units and any design or build defects built in at the factory.
Gary
