I am wanting to change the lube in a transmission I am working on. Its a FS-5601a 6 speed in a 1993 topkick. Has a PTO mounted on it. The manual shows different options on what to use to fill it. First it shows the CD50 synthetic transmission fluid. Also shows HDEO 40w and 50w and also GL1 90w gear lube. The synthetic Im sure would work well but is expensive for a truck not used much. The other options seem hard to find around here. I can find 30w and multigrade diesel oils. Do I need to just pay for the synthetic or does anyone know of other options for this tranny?
2001 Chevrolet 2500hd 8.1/Allison 2011 Ford Explorer 3.5