When shops perform an automatic transmission flush, as a matter of routine, many will include aftermarket supplements in the procedure. In fact, I once had an independent shop perform a flush which included the removal the factory-fill ATF and the installation of AMSOIL Synthetic Multi-Vehicle ATF. After the AMSOIL ATF was installed, I stopped the tech as he was about to pour an anti-shudder additive into the transmission. I asked him why he was adding this product. He said that they include this product with every ATF change. I politely explained that I had opted for a very sophisticated ATF and that the anti-shudder additive was not needed. He asked if I was sure and I indicated that I indeed was.
Aftermarket ATF additives are used as an attempt to help marginal ATF’s meet certain OEM specifications or to “improve” performance characteristics. The idea for many shops is to use the cheapest fluids possible and then “top them up” with treatments to prevent any performance issues. AMSOIL has released a technical service bulletin called, TSB: Automatic Transmission Supplements, which shows that many of these additives actually have a detrimental effect on performance and wear resistance.