Can't really tell if you need a new BB or not, but if you do, get a cartridge one and not a "vintage" cup and loose bearings. While loose bearing BBs can last for a long time (my 22-year-old 7400 with > 50K miles is still going strong), you'll likely have fewer problems with a good cartridge and they don't need as much maintenance.
The Dura-Ace 7400 cranks require a 68x112mm axle (or 70x113mm for 70mm BB shells). The 103mm axle is for the 7410 (8-speed from early 90's). 68x112mm is not a common cartidge BB size but 68x113mm is and should work.
Last edited by Gonzo Bob; 08-07-08 at 12:16 PM.