Scott,
Your findings are similar to mine! I thought I was losing my way when somehow AC Delco's website doesnt seem to be carrying any engine cleaners, let alone something called X-66.

And yes, there IS this GM product called "GM Top Engine Cleaner".

So are we talking about the same product here? Gee....this engine cleaner is getting really elusive, must be some kind of "magic" potion.......

Mervyn
1983 W126 (280SEL)
PS. so far still no luck with online stores carrying this item.