I know that the metzlers that were on my LS when I first bought it passed inspection - no cracks on the sidewalls, plenty of tread, but they were old, and really the rubbers wasn't as pliable as it is supposed to be. Those tires were very slippery and not confidence inspiring if leaned over very far, and were promptly replaced - I now have no worries about leaning the bike over as far as I dare, and it runs straight and true, no wobbles, and sticks like glue. Maybe it is worth just changing your tires anyways. I know that I never have tires last that long on any vehicle I own, so I don't generally have that problem.
Oh, and no, the grease would not revert from a hard, dry state (if it was) back to a soft, pliable state unless you managed to do something to raise the temperature of the steering head up to about the max temperature of your kitchen oven - and even then, it wouldn't be consistent. Pay close attention to road surfaces, temperature, and weather conditions and note when the bike handles well or handles terribly. I am betting it is the tires