Planetary Herbals makes a formula called Myelin Sheath Support. Don't know how well it works, but the company was founded by one of the premier herbalists and Chinese medicine docs in the world and the product has been available for many many years. It has a whole lot of ingredients -- minerals and a host of herbs -- so the ingredient panel alone might give you much room for research. If you contact the company they should be very helpful. Your information about St. John's Wort is correct. It's primary usage historically is for nerve support, both in homeopathic and herbal form. (It's second most common usage is in anti-viral formulas. It's usage for depression is much more recent). For this purpose you probably want the tincture, not the standardized extract, as the standardization is for what is suspected to be the main factors in depression aid. There are formulas for nerve support. Try Herb Pharm for this. Whether it can repair the damage I have no idea, I've used them for current nerve pain, not for damage. Again, reading the labels of Nerve Tonics by well-regarded herb companies can give you a good basis for research.
Methylcobalamin B12, Centella asiatica (gotu kola), Lion’s Mane Mushroom (Hericium erinaceous), Ashwagandha (Withania somnifera).
there are many herbal protocols to kill the infection. But - killing the infection does not repair damage left behind. Just stops more future damage.
I have yet to find an herb that helps the body repair damaged nerves, from whatever the cause. Its got to be out there, I just have not found it yet.
Dr. Klinghardt, Dr. Dietrich Klinghardt M.D., PhD
http://www.klinghardtacademy.com/Protocols/Klinghardt-Biological-treatment-of-Lyme-disease.html