I had a shop do mine with a few other thing's but I'm planning on taking them off Odo and switching them to the new toy. Since it's at the top of the system I would think fluid loss would be minimal and you could just add a little to the expansion tank or the rad . Just my 2 penny's .You should replace the plastic 3 way at the same time .If I got one of those breather fittings for the heater core, could I install without having to drain/refill? The breather is specifically so I can burp it and not have to mess with all that, right? I just had my radiator flushed about 8k miles ago.