From my experience, you may, remove things that could lock your machine from the easier ones to the more difficult. Here is my "method " :
- First at all try to put some kerosene instead of oil and try to run your machine, if it solve the problem oil it.
- Remove shuttle and needle
- Verify if the lock symptom is always present with different stitch lengths
- Remove needle plate and verify if there is nothing in the feed dogs
- Verify that there is nothing wrong in the movement under the bed
- Remove the face plate and verify that there is no gummy old oil on the needle bar
- Open the two inspection plates and verify that these areas are clean. Look also if there is no loose screws.
Some parts are easy to remove like the take up lever, and you don't risk anything with timing.
And oil, oil, oil ...
There was my two cents, I hope it could help you.