Just my two cents: if you are not sure it is the bolt you removed, you must measure the depth of the hole. There is a pivot of the chain tensioner inside that restricts the depth. This bolt is not holding it really, but needs to have the correct length.
I used thread sealer on it.
Also: I think I read somewhere that this bracket is used as a hook point for engine hoist, when you lift the engine. So the bolt is M10 if I recall correctly. Not sure if I remember it right...