I bought a stylus h second hand that was supposedly used only a few times. It's an awesome machine but under 12volts it's too slow for me. I was told that it's safe up to 13 so I've been running it between 12-12.6 volts for color and fine lines and it's fast enough but after an hour or so it will slow down suddenly and then speed back up after a minute or two.. I only use ttechs and I have cleaned and put a little super lube on the ball at the end of the bar that pushes the cart thinking maybe it was a friction thing but I don't think that it's made any difference.. I use a critical cx1 and a deathless elite RCA cord so it shouldn't be an issue with the power dilivery to the machine. I have over 10 other rotaries and none do this . Any suggestions?