One problem related to front suspension wheel bearing has been reported for the 1998 BMW 540. The most recently reported issues are listed below.
Driver-side front wheel bearing makes noise when wheel spins freely. This was reported several times to dealer in past. Dealer replaced passenger-side front bearing ! driver-side beraing still noisy. Waiting for complete failure to prove dealer wrong. Front wheel bearings are marginally designed for BMW 540i, this is well documented on various web sites of BMW owners. Bearings last 75,000 miles!.