Don’t they have a water hose or a bottle of water with a spray? Next time, open the hood and with a strong light take a look at where the water has splashed to get a clue. I’d maybe suspect something like the crank sensor that is lower down. Then in the driveway, you might want to use a water bottle and spray water carefully in the various places until you can get a hickup from the engine. Then back to the shop with your results.