UPDATE:

For those interested, the problem is finally resolved. I was the thread
starter, asking about an intermittent parasitic drain that can't be
found. I finally isolated it to the alternator; and today, after a day
of trying, finally got the alt off. Brought it to a shop, and they
diagnosed the problem as "grounded rotor". Regulator, diodes all
checked out fine. They replaced the rotor with an identical (Nippon
Denso) rotor, and now there is optimal current drain and no parasitic
load. Total cost, including labor (if converted to US$): $24.

Thanks to jim, TeGGer, Earle and all the others who replied. More power.

 

UPDATE:

For those interested, the problem is finally resolved. I was the thread
starter, asking about an intermittent parasitic drain that can't be
found. I finally isolated it to the alternator; and today, after a day
of trying, finally got the alt off. Brought it to a shop, and they
diagnosed the problem as "grounded rotor". Regulator, diodes all
checked out fine. They replaced the rotor with an identical (Nippon
Denso) rotor, and now there is optimal current drain and no parasitic
load. Total cost, including labor (if converted to US$): $24.

Thanks to jim, TeGGer, Earle and all the others who replied. More power.