I've modified two flashes for UV. None of them were SB-14, and I had to cut off the front windows to reach the xenon tubes. The yellow coating was very easy to remove using metal polishing compound. Cymbal cleaner works well, too.
As you should already know, the xenon tube is very delicate and vulnerable. Any excessive force will damage the tube, and cause the explosion of the tube. Just apply the polishing compound on the cotton swab and rub the tube gently. No need to force it. Wearing a pair of protective goggles would be preferable.