I have a 2012 Heritage with 3500 miles on it. I check oil every couple of weeks. Today I checked the oil and had to add about 3/4 quart and this has me concerned. Around ninety percent of my riding is local non highway. No apparent leaks and I am using Syn 3 since the 1000 mile service. Bike runs great. Oil looks dark to me for 2500 miles on it but I am no expert. Should I be concerned?