Unfortunately because of hysteria, old information, ignorance of the effectiveness of current inspection protocols and, quite frankly, dive shops creating a potential market for new tanks by falsely condemning 6351 tanks in the name of safety, it is often hard in some areas to get a fill for any tank older than 1989 or so, whether it is a Walter Kidde, Luxfer or Catalina (which again has always used 6061-T6 alloy in it's tanks and never used 6351-T6 alloy at all, making SLC a non problem).
My thought is keep the Walter Kidde and find a better informed and/or more honest LDS. If they are ignorant or dishonest regarding tanks, it begs the question of what other areas of diving expertise or equipment may suffer from a similar ignorance or lack of character.