We run semi-synthetic (Trim MicroSol 585XT) I need to get a skimmer, but cannot decide on belt or disk style. I have space for either style. What is the benefit vs belt or disk? Obviously the belts wear out, but so does the wipers on the disk style. I have a skin that forms on the coolant surface, not sure why. So not sure if a skimmer will work for that. Does anyone else see that skin on thier coolant tanks?