I rebuilt my 20k (6S ecu also) about a year ago. I just stripped it down and had the rods turned down 10, mains were fine. Had my machinist order me some ACL Race bearings, about 100 bucks for rods and mains. Threw it back together and it runs like a champ. Havent had a problem with it since and Ive run it hard. I think it has to do with the fact that these motors are at least 10yrs old, sitting for who knows how long, and who knows what happened to them before you got it. A little motor that puts out almost 150hp per liter and revs to 8k wont last forever. I figure if I get another 30k miles out of this motor its worth it to me.
AND- If you do want to even think about rebuilding it, DONT RUN THE MOTOR AT ALL! Damage has already been done, dont make it any worse.