leaky toilet

I have a new toilet that was put in about three weeks ago. Last night it started leaking around the base. Not having time to sort it out I just called a plumber to fix it. Well, that was fixed, but now it's leaking from one of the mounting bolts between the tank and the bowl. I tried tightening it and that helped a little. I tried taking the bolt and rubber washer out and re-seating them, but that made no change. Is there anything easy that I am forgetting to help this seal, or is it just a continual hit-and-miss type thing? Thanks.
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