I had the same issue on my W140. The right front tire was wearing on the outside. After two alignments didn't fix the problem I took it to the dealer where they diagnosed a bad wheel bearing.

__________________
"It's not about how fast you can go, but how well you can go fast."

Bob in Richmond

'97 S320 (LWB), Ruby Red Metallic, 73k miles
'97 S420V, Smoke Silver Metallic, 155k miles