Oh, so it's the "Gil bracket"? Gil is the manufacturer. Bracket, meaning the "engine bracket". OK, now it's clearer what you're asking.
Sure, filling it up is one way. Although if it's "filling" up (and staying full even when on a trailer), filling it with water isn't going to help.
You may not have re-sealed the access plate well enough. Not sure how you did it. There's a rubber o-ring that needs replacing and the circular ring needs to be sealed (including the screws). This is the most common spot to leak.
The Gil bracket, by the way, is hollow where it mates to the transom. Meaning, water can leak in there in between the transom and bracket. If the leak is near the top of the bracket, that would let water accumulate.