With CCs any logic board from a 520 or 550 (or MacTV) is plug and play.  If you can find a known good one of those before you get your stock LB capped, you can determine what else might be wrong. The ABs on those don't have caps that are any younger or sturdier than the LBs'.  If you want it to work for a long time, you might as well replace every capacitor in the box!