Ferdman, you must be right about the voltage regulator!!

Today I had the chance to monitor my idle while I've been in an hour traffic jam.
I was raining, and I noticed that whenever the wiper takes a round, my idle drops 1-2 hundreds, and also the oil pressure goes down from 2.2 to 1.8. The moment the wiper is steady again, it all goes back to normal. I could clearly see dashboard lights are faded away for that moment the wiper works, so I'was pretty sure that my charging at hot engine is low.
Stopped by and checked at the battery, and bingo, it was 13,6V with lights on, idling, and only 12,3V while the wiper's licking along the windscreen.

I'll check the voltage regulator brushes tomorrow, and hope for the bests. WIll post results here.

THanks again, Ferdman, you're awesome!