Yeah that mirror trick is smart. Reminds me of when I had to check for a coolant leak behind my engine block. Rigged up my wife's compact mirror with a zip tie to a coat hanger, looked like total junk but I could finally see the drip path. Ended up using a long plastic grabber tool meant for picking up trash to twist the hose clamp tight.
Grab one of those small inspection mirrors from an auto parts store and stick it to a welding magnet next time. Lets you position it anywhere on the block hands-free and still bend the neck to see around corners. Way less shaky than a coat hanger rig.