ABS not working

A few months back I was driving in a spirited manner in the country and I managed to get a mild lockup on one of my front tires. I felt no ABS intervention but since the brakes are powerful I just chalked it up to an older system that allows a little slippage. But it stuck in the back of my mind. I have a 1993 512TR Japanese spec w/ ABS. I almost never drive her in the rain any more but I had to yesterday so I decide to take the opportunity to test the ABS again in wet conditions so as not to incur much tire damage. And it locked up. I could feel the 4 wheel skid. As i came to a halt I could hear the ABS motor(I think I heard it). I also note like all older ABS you can hear it cycle when I pass maybe 20 km/h or so so I think the motor is trying to do something. The ABS light only shows up at startup which is normal and if I press the ABS kill switch so the lamp and normal car diagnostic seem to work but are clearly missing something. Maybe 2 years ago I had new endless brake pads put on and bled the system with Ate Blue fluid. The brakes are strong and work fine except for the ABS. Any ideas guys?
Thanks in advance.

 

No ideas anyone?

 

I'm traveling in South America at the moment but I'll have them looked at when I return over winter.

 

A very late response here but had the ABS diagnostics and all fine. I drove in the wet last night as I had to unfortunately and did a quick test and yeah the ABS works fine. i think the time I got a bit of a lockup I was driving quite rapidly on an uneven road surface and just one wheel probably hopped and the ABS system was just too slow to catch it. All is well!