The presser foot pressure system on the 301 is designed for some weight savings. On other machines, e.g. 66, 27, etc, there is a solid bar top to bottom for the presser foot, with a large spring around the bar which is compressed via the pressure screw.
On the 301, similar to the 99, there is a partial bar, from the foot itself up to the guide clamp (held on by a set screw). This bar is hollow at the top, the spring drops down into this bar and then there is a hollow metal tube, closed at the top end, which drops over the spring. The pressure adjuster screw goes over the top of the tube and when screwed down pushes the tube and the spring downward, putting more pressure on the foot.
The spring itself is not actually exposed to oiling. With the adjuster screw fully removed, the spring is either fully extended or it isn't. If it is not fully extended this would actually result in there being less pressure on the presser foot, possibly, unless you adjust the screw all the way down; theoretically the screw could be all the way down and bottom out without putting full pressure on the spring, but this is highly unlikely.
With the adjuster screw fully removed, you can remove the tube over the spring just by lifting up on it. The tube may lift off separately to reveal the spring which should lift out.
There are two contact points for cleaning/oiling: 1. where the bar goes through the shaft in the machine body, 2: which the guide piece, which has a polished arm, rides in the machined channel on the back side of the machine, near the presser foot lift lever.
With the adjuster screw fully removed, you should be able to lift the presser foot, by the foot, and release it and it should freely drop back down. If not, then you have some cleaning/oiling to do.