Sometimes those old timers are the worst at being able to adapt to the new methods and strategies of working on late model cars. Things aren't like they used to be. He may know his chit, but you need many special tools but most importantly- lots of ingenuity these days to R&R even the simplest of things like a speark plug. Not sure why yours would be any different, but I'll believe you (him). Sometimes the easiest things can be a motherf*cker. Just depends how your day is going.
I wasn't talking about you f*cker
Yes you can buy Dexcool just about any parts store. You can mix different brands of Dexcool, but not different TYPES of colant. For example, you cannot mix Dex with green coolant.