2003 Volvo S60

The fluid is a synthetic oil from Volvo and can not really think of an alternative fluid you can use. Also when changing the fluid in the transmission, you need to have some sort of scanner that can get into the transmission control module to reset the oil counter. Now if you are having issues with the shift quality, I would not recommend flushing the transmission. Most likely you may have an internal fault with the transmisison or valve body or an issue with the transmission control module? I would recommend that you go to Volvo and maybe see if there is an upgraded software available for the transmission control module. Normally the software will take care of some issues with the shift quality but does not really work 100% of the time. In my experiance, it ends up being a faulty transmission.