We recently saw this question asked of Spectro Oils and wanted to share the info with you all, as we found it very inofrmative. If you have any other specific oil or lube question be sure to head over to Spectro’s site, as they do a great job keeping everyone informed and up-to-date on certain products.
Spectro 6 Speed is GL5 rated but is safe to use in GL1 applications. We use a different formula (developed by Spectro) than other brands that is buffered, this formula will not attack “bright” metals such as brass, bronze and copper found in older transmissions. It’s more expensive to produce, but we feel the performance is well worth the cost. It also improves shifting in most applications, reduces noise (5th gear whine in HD 6 speeds) and is highly resistive to shear and loading.