I would replace the Condenser Fan Motor.
Loudness would be attributed to either bent fan blades and/or worn bearings. Considering the age of your condenser unit, it is most likely bearings. Typically, the bearings on a Condenser Fan Motor do not require lubrication, because the bearing packs are sealed.
- A video on removing a Condenser Fan Motor can be seen here and
- A very in-depth and high quality video can be watched here.
Here is a picture of a generic Condenser Fan Motor:
It is essentially sealed. This is on purpose. It keeps the dirt and debris from getting into the internal fan motor components. The bearings are also internal. There would be no effective way to lubricate them without literally removing the rotor from the stator (i.e. taking the fan apart).
Even if you do take it apart and remove the bearings (there is one in the back and one in the front) there is a good chance it is going to look like this:
In that case, it wouldn't be very wise to try and remove the protective jacket covering the bearings. They aren't too expensive and could be replace very easily. Just get yourself a puller and you would be all set.
If you are lucky, your bearings would look like this:
If your bearings do look like that, then it would be a lot easier to lubricate and probably wouldn't even have to remove them from the rotor in order to do it.
I would still replace the fan motor. It is old. It has been exposed to the environment for a very long time. Plus, technology has dramatically improved and you should be able to find a suitable replacement that is more energy efficient.