When you replace that I would also take a good look at the harness going down to the battery for a short, frayed cable etc.
I don't know if it's specific to Merc (haven't seen it on other motors), but when the power that the rectifier produces has "nowhere" to go, things fry (which is why you never start a Merc that has a rectifier without a battery connected even if it has a pull start).
So make sure the path to the battery is working properly and the battery is there. You don't want to change all the "guts" and have it happen again the next time you fire it up...
