hi there..........being an ex stannah service engineer this was common for marks to appear on rails so do not worry,,and you are right that they are dry nylon rollers,,,on annual services we used to clean both tubes with amberclen foam cleaner, but you must always dry the rail tubes off before running the stairlift as the rollers will pick up any dust particles and compress it into rollers which will eventualy leave these marks on the rails... hoped this has helped.......ian portsmouth uk
IAN
March 2012
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