I'd pull and clean / lube the entire distributor.

This is probably a "standard" Bosch distributor so pics / vids of most any Euro German centric car ( like VW / SAAB / VOLVO ) would be similar.

The plate where the points attach is for vacuum advance, the distributor rotor shaft leads to the mechanical advance.

You can check for the vacuum advance sticking by pulling the dist cap / rotor / plastic cover ( not all have this or it might be missing ) then applying vacuum to the canister and checking movement. Also be sure the ground wire is intact between the moving point plate and distributor housing. Old grease ends up insulating the two plates a bit and the loss of a ground wire can lead to a missfire.

When you remove the rotor, there will be a felt circle stuffed in the hollow of the shaft, this is an oil wick to keep just one part of the mechanical advance lubricated. You should be able to turn the rotor in one direction and have it spring back.

Generally there are 2 types of springs in the mechanical advance system, a small diameter wire with round eye ends and a larger diameter wire with one oval end / one round eye end. These springs make a 2 step advance where from zero to below idle RPM the timing is retarded to allow for easier starting then a flat spot in the advance curve to promote stable idle. If this flat spot was not there, a slight increase in idle speed would result in increased mech advance that would increase idle speed and result in more mech advance.