The black plastic thing you're describing is the ENGINE COVER.
Although the Isuzu schematic (item #35) doesn't show the grommets available separately, I'd still call Merlin and ask anyway.
Or maybe try a hardware store to find a thick rubber washer or grommet, something similar with same OD and a hole. Even if it's not as tall as the original, I think it would hold it down...or put a little earthquake putty on it....it's my version of duct tape!
I think it could handle the heat.
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