My father-in-law, who has owned MANY Bonnevilles, and Chieftans, Starchiefs, Parisiennes (sp?), Granvilles, and you name it, had an 05 SE for about a year and got rid of it because he had it back at the Dealer every few months. Now he has an 06 GP, but I think he would rather be driving a Bonnie.
But, I woudn't worry too mcuh about his probelms with his 05, any car model can have one or few slip through with problems.
And, I didn't see anything, so is this an SE, SSEi or what.
Oh yeah, and i can't believe no one else has sait it....
As far as buying the 03, I say as long as you are happy with it and the price you are getting it for, go for it. As mentoned, when and if any problems arise, you'll have plenty of help here getting them resolved.