So I've been looking through a the forums and haven't really found a clear answer. I have a 1985 Toyota Celica Supra with 240k miles never rebuilt still running fine with minor oil leaks. I'm planning to do my first oil change since I bought it and am not sure what type of oil the previous owner used. I've had a few people tell me to be sure to use an oil with zddp added. After doing some research it sounds like I should be using a high mileage version of oil. But most of the high mileage oils seem to be synthetic? I though switching to synthetic in such an old engine would cause more leaks? I'm thinking of M1 high mileage, Valvoline MaxLife or maybe Royal Purple HMX? The only concern I have is that these are all full synthetic. My question is what oil would you guys recommend thats for high mileage engines with zddp added? 10w-40 range.