How to drain voyager manual gearbox?

I found out that the gear box oil of my '98 has turned into black sludge
(it's 5 gear manual tranny). I decided to change the oil, but can't find
where to drain oil out. Is the hex bolt under the tranny the drain plug?

The user's manual recommends to use mopar's own lubricant (mobil's
product) or SAE 10W30 motor oil. Parts store guys checked their mobil
manual and it told to use 5W40 fully synthetic motor oil. Any
experiences on motor oil in tranny? The gears are quite hard to shift,
especially after cold start. I want to get rid of this problem and
thought that here at north where temperature drops below -25 deg. c, it
might be a good idea to use synthetic instead of mineral oil that
Chrysler uses.

Lubing the levers leading from shifter wires to gearbox helped a little
bit, but I hope changing the lubricant would solve the hard shifting
problem.

One funny thing I've noticed when checking levels on my Neon and
Voyager; the both should have the oil level reaching to the filler plug
hole level, but they've been overfilled ad the factory; when I pulled of
the plug, the both flooded oil quite much. Maybe they fill some extra in
there at the factory?