I met a neighbor of my brother-in-law who had a '92 SSEi. We chatted for a while and in his conversation he mentioned that when he got the car it ran great. Recently, however, he was trying to save money by purchasing 87 octane and adding 104+ to it (an octane booster). After two tanks, his car began to knock and his plugs became very fowled. I don't know whether it was the additive or whether he was just abusing his car in some other way. I play it safe and run the 92-93 super unleaded.
This probably doesn't help you, but I thought I would share it anyway.
Retired Moderator, The Bonneville Club www.bonnevilleclub.com
RIP Oldsmobile, April 29
1995 Bonneville SE Supercharged (Stock)
Current Mods: Dirty GYM Sock air freshener.