ABS repair options 90' 240sx SE?

[jerryk]

I just purchased my second 90-240sx se fastback stick with 175k on it. My other 90 240sx with 210k is suffering from severe rust underneath and will be the parts car. Both cars have identical features except for one. The replacement car has ABS that is leaking from the unit, near the passenger side firewall under the hood, but otherwise seems to be working. I saw a complete rebuilt replacement for $600.00+ but I do not think that is necessary it just looks like a seal problem. There are no trouble lights on the dash. Where exactly do I find the diagnostic unit to view trouble codes I printed out the list of the codes. How do I go about fixing the leak? Are there any other Nissan year models and make that I can use?