If you do any research into this issue the fluid the trans is made to work with has exactly whats needed, if you use other fluids they actually break down the glue that holds the friction material on the clutches. Not actually a good thing on any transmission let alone a tired one. You might get lucky and get a month or 6 months out of it with "other" fluids. The 540 trans is just one that happens to require the expensive stuff.