if you can get into fuel tank you can do so many more interesting things. chlorinated solvents will burn giving hydrogen chloride, and this will corrode everything downstream, pretty fast at that because it’s hot

also if you can fuck with fuel tank, you might be able to do the same with engine oil. fine alumina or silica added to it will cause quick weardown of moving parts that at the same time looks natural

not sure what kind of (permanent) damage water will do to engine, maybe it’ll look like it’s flooded if enough gets in