Golf tail light problems

Noticed right tail light is not working on a 96 Golf. Obtained bulbs
and went to replace. The existing (2) right tail bulbs appeared to be
ok. Further investigation showed that the right brake light and reverse
light are not working either. The right amber turn signal works, but
the brake light also flashes very dimly--suggesting a ground problem.

The left side cluster appears to have all bulbs working ok, and the
center high stop lamp doesn't work at all.

I turned on the running lights again and tested voltage at the right
side tail light bulb. Nothing. (The left side showed voltage, of
course as that bulb was shining.)

The left side bulb holder has numerous connectors attached to it
(perhaps leading to the right side and center brake light).

The right side has just two plastic wiring connectors plugged into it.
One has a single wire and can be removed. (There is slight corrosion
visible.) The main connector which has many wires wouldn't budge. I
think it may be corroded together and I can't remove it. Does anyone
have any suggestions on how to remove this without harming the wires or
bulb holder assembly? I'm hoping that the electrical problem will be a
simple case of corroded connectors.