I'm a little confused with your description... are the wheels binding after the front set screw was gone or before? The bevel gear is pretty difficult to break so I'm more inclined to believe thats its the internal diff gears... They are made of a soft metal thats easy to break.. also, the diff carrier is pretty fragile also... these are more likely the problems...When your new center cup comes in, it should include the set screw... they are 4-40 set screws... look for them in the dubro section of the hobby store.. lastly, the diffs don't use fluid, they are filled with regular grease... just use one that sticks to gears.. automotive grease will fly off the gears.. tamiya makes a good one..