I have been avoiding the upgrade due to the inconvenient attic location (cool and dry) of the WAP11

Whoa, whoa, whoa... you didn't say you installed the device in an attic.

That could be the whole problem. I once had some wireless equipment installed in an attic, and it failed at the same time of day every day until I moved it indoors. The extreme temperature swings in the attic were what did it.

You say your attic is cool and dry, but does it maintain a reasonably constant temperature all day? Somehow I doubt it's climate controlled.