XDJ R1 pitch slider problem

I have an XDJ-R1. Overnight, for no reason, the pitch slider on one deck wont sit at 0.0. it sits at 0.12+ sometimes 0.16+. I only use it to play CDs / USB - it has never been connected to a computer. Firmware is up to date. Even with no CD / USB attached it wont zero 0.0 on the right hand pitch slider. I have it set at 6+ and does go up to 6+ and down to 6- with no issue, just wont sit at 0.0 and fluctuates.  Could it simply be a dust issue or similiar? Any ideas to resolve the problem would be much appreciated...