my piece of mind. When replacing the xmission and diff fluids I went to Redline products. The MT90 eliminated the gear grind from 4th to 5th. I eventually trashed the transmission and replaced it with a new 99+ spec from Z1. After breaking in the new transmission I flushed and installed Redline MT90. Have about 3000 miles on it without any issues, loses or concerns. Good luck resolving your issue