There have been a grand total of ONE-TWO '98-00 LS400s with possible ECU issues reported in the years i've been here, and only in one of those was the issue even remotely affiliated to capacitors.

Personally, unless there has been a problem that all other levels of troubleshooting have failed to fix, or there is visible damage to any of the caps, I wouldn't tear apart a perfectly working '98-00 ECU. (or any other ecu for that matter, though the problem is more common on '89-94 cars than any other generation)