I just purchased 2 Sonetts-- both been sitting for years and need restoration. I intend to use synthetic lube in the gear boxes. 5 yrs ago I bought an S-10 p/u that would not shift w/o double clutching. Thought I needed new synchros-- but I put in Amsoil synthetic gear oil and the trans began shifting like new! It was great. I added another 50,000 miles to it before I sold it. I am sold on synthetic gear oil. I run it in my wife's 900s as well.(posted 8458 days ago)