I'll try to make this short and sweet. I recently purchased a 1985 Honda XL600. This bike is an air cooled, single cylinder, enduro style. The bike has 11k miles on it. The guy I purchased it from, said he took really good care of it and as far as I can tell, it is running really good. Matter of fact, it has always started on the second or third kick start. Anyway, my son has the exact same bike, except it is a 1983 model, but basically identical except for cosmetics and it also has about 11k miles on it. This past weekend, my son had to tear into the bottom end of his engine to replace an O-ring and a seal. When he had it opened up, he found and cleaned out some sludge. I think it was common for folks to run 10w40 dino in these bikes. Finally, my bike is in Phoenix and I will be riding it back to Colorado this weekend, doing two, 400 mile days. Before I leave Phoenix, I am going to really go over the bike from a wrench twisting perspective, along with an oil change, air filter cleaning, etc.... These 800 miles will be a good chance for me to pour in an oil that will be really, really good at cleaning up the engine. So here is my question.... What oil should I pour in? It needs to be easily accessible (Walmart or auto parts store), as I don't have time to mail order anything. I am leaning toward a synthetic and wonder if a DELVAC or Rotella would be a good choice???? Upon arriving in Colorado, I will dump this fill and go with DELVAC 1300 15w40. (becuase I have a bunch of it on-hand) Anyway, what are your thoughts and recommendations?