Error 16 is related to the date and time. Your clock capacitor has likely spilled it's guts, very common with all but the 1.6 models. When the clock capacitor spills its guts the electrolytic fluid often if left unchecked eats the traces in the area. Sometimes it's not so bad and sometimes it's a rough repair. It's way past time to recap the whole mother board, possible even the psu.
Also original xbox mother boards can suffer from "trace rot" often found around the edges of the mother board.
If it were me I'd start with all of that first. Weak or bad caps can cause odd issues because they interfere with the voltage consistency, dead caps obviously more so. :) If after clock cap removal (and area repairs if needed), and after a recap of the mobo, the dvd drive still plays funny then the shift the focus to it.
It won't do any good to obsess over fixing the dvd drive while the console is being disintegrated by clock cap electrolytic fluid, and other caps are failing from age.
So basically it's time for a full diagnostic and refurb. Good luck.