Prior to the Bonneville Club website, there were a couple of Bonneville forums on YaHoo. I seem to recall reading that dealers were using 5-30 synthetic oil to top off the Bonneville superchargers.
Following their advice, I started using 5-30 Mobile One at around 70,000 miles on my 1992 SSEI. I now have 140,000+ miles on my car and the supercharger runs fine. If there were problems using 5-30 M1, I would think it would have showed up by now (or, maybe Iím just lucky?).
1992 SSEI/140,000+ miles, stock