Just had an Aqueon Pro 200W start leaking water into the heater from the bottom. I was luckily next to the tank. Heard some odd bubbling noise and an odd smell. Run over start powering things down to see what was up. Tanks off, noise persists. I look at the heater to see bubbles rising out. Took it out right away, what a smell...
I had bought it used so I don't know how old it is.
Lesson learned, I don't think I will buy used heaters just for the knowledge of their age.