[gearby]

That was really deep water if water was sucked into the airbox. How the electronics werent shorted out is beyond me. Flood damage is long term trouble.
Here's your problem. A piston that has been hydrauliced (spelling?) Certainly can bend a rod and most likely will. If the rod isn't bent very much it will just produce a low compression state which will be very difficult to detect on a V8 motor because you have 7 other cylinders firing correctly. It doesn't mean that the cylinder that got hydrauliced is a dead cylinder. There's no real way to tell without a compression test. If the cylinder is in a low compression state though it has to be repaired. You could have a future major repair if you don't fix that.
I rebuilt a Dodge motor that had hydrauliced a piston. The rod was bent so bad that the piston skirt was hitting the crankshaft counterweights. That's how much the length of the rod had been shortened.
I do own 2 BMWs and I've worked on others. I do own the master Vanos tool kit if you want to tackle this on your own. It will be an adventure. ;-)