Hi Greg, The oil capacity is 3.5 liters, not sure what that is in quarts. I just bought an 81 750 ltd. Actually its been about a month ago now, i have been thinking the same about Mobil 1 syn. I found one site that said you shouldnt put it in older bikes but gave no references as to why. There is the belief that it causes leaks, but if it does its because it cleans out gunk that is preventing worn seals from leaking, better to have a leak than gunk in your engine. I dont know if by older they took into account mileage. My bike has only 10k on it. I havent switched the oil yet, I havent been riding but spent quite a bit of time on the carbs and rebutlt the rear master cylinder. I have a manual I bought on line,Its on disk and was only 7 bucks. I forgot to order filters so i havent changed my oil yet. I have the mobil one and also castrol syn. blend, thought I might start with that one first, let me know how you make out and if I can be of any assistance let me know. Byron