Your original description reminded me of a recent problem I had with a different movement. I switched screws.......The head on the screw holding the pallet cock turned out to look the same, but had a minutely thicker head. This caught the balance and stopped it. I felt really silly but it was a very rewarding fix!
If you didn't clean the balance jewels introducing fresh oil could dislodge the old gummed up oil and make things worse.
I'm afraid you you wont make much progress without cleaning the balance jewels.
Assuming you have checked that all jewels are clean and balance pivots are not bent bu the problem still persists,... I would check the endshake of the balance. A watch this old may have had the balance staff replaced and the replacement may not have been an exact fit. On most watches you can adjust the endshake a bit by pushing the jewel housing in the mainplate up or down a bit (using a staking set). Note that this may change the interface between roller jewel and pallet fork so this needs to be considered.
On larger mens watches you can sometimes get a screwdriver between the hairspring coils to remove the jewels but on these smaller ladies watches its not so easy.
Hello all, Imnew to the group, been collecting for only a short time. saw Marks youtube vids, and gave a crack at the basic course. I've retired from the open heart team and very used to working with loops on mm objects. This subject of watchmaking has always interested me, but family and work always to precedence.
I have a Solution - Clear nail polish
Find an inconspicuous spot then under magnification put a small drop on the tip of a pin and try to mix it into the plastic.
If it polish changes colour you have your glue if not, let it set to see how well it adheres anyway.
If above fails try another brand - nail polish is just a solution designed to dissolve shiny plastics an their additives.