I have a one year old Yamaha Xeno YSL88OG, and I've notice a slight grittiness on one of the slide tubes. I've cleaned and flushed the outer slide, but the abrasiveness remains, despite using various slide creams and lubricants. I'm concerned that there is corrosion on the inside of the outer slide. Bearing in mind that the instrument is only one year old, I'm a bit disappointed with this. Is the inside of the outer slide coated with anything, and what are my options in terms of getting this repaired? Thanks. Andrew.