Any lump or bump persisting for such a long time should be seen by a dermatologist. Any brown spot on lip line can be due to ultraviolet rays of sun which penetrate the skin. They can just be liver spots that develop with age. A clinical examination is essential and you should consult a dermatologist. If the spot is an age or sun spot it can be treated with laser therapy, which will correct the discoloration and irregularity of the tissue to diminish the spot's appearance. Treatment will depend on the underlying cause. Hope it helps.
Best wishes and regards!
Sometimes it may cause due to vitamin deficiency or problem related to liver. It may need to be cure internally rather than applying any product on your lips. It may cause more damage than help. I suggest you to consult a doctor than experimenting with products available in the market. For Vitamins deficiency you eat a lot of fresh vegetable and fruits and go for some medical test to confirm whether you have any problem related to liver. A good doctor can guide you to select the tests. Hope you will be cured soon.