Vinegar flushing a 22 year old hot water heater

This is a direct oil fired hot water heater. Symptoms are it doesn't seem to have as much hot water capacity as it used to. I've done many plain water flushes but trying vinegar, per the manual and lots of stuff I read online. This attempt was a 1 hour soak followed by a flush.

Видео Vinegar flushing a 22 year old hot water heater канала kevin9c1