Another vote for dry solder joints on the ABS module - well worth checking out before you start throwing money at sensors etc., it's a fiddly job but very low cost, mainly just your time. Look in the "Technical articles" section, there's a how-to-do-it in there, and lots of other threads on here that cover the same thing. If your reluctor rings are really crusty it's worth replacing them, but faulty ones often don't put the ABS light on, as the module just thinks the wheel is skidding, not actually a fault.
Cheers!
