Hi i have nearly the same problem,ABS starts working when car slows down till 20-10mph.
checked on diagnostic no foults
at the end i found Rear ABS rings damaged of rust
i was looking on ebay,amazon and web
no chance to find
Lexus dealers doesn't sell them,they just offered full driveshaft for 250£.i need bouth sides total 500£
can somebody help me or any sugestion where to finde ABS rings
gs300 mkll 99
thank's