Obviously we have to start off with the fact the Cybertronians have been around for MILLIONS of years, far before the creation of sentient cars and the Autobots & Decepticons have been at war for 8 million years. I would have them in their own sector somewhere in the Unknown Regions, since it's mostly unknown for that reason and people don't bug them. Also yes Unicron, The Primals, & the Insecticons exist here too since we're doing this.
The Galaxy would be in for a shock that giant sentient robots have existed longer than them and can transform into vehicles and have their own war going on. As for the Autobots, I'd imagine they would want to help out others but also don't want to multitask fighting two Wars either. Thankfully they can still get their friend to head back to Cybertron anytime since they're not the one trying to conquer and burn worlds like the cars.
The Decepticons would still try to track them down and since the Autobots got to the main Galaxy first, they could easily tell the Galaxy the facts just in case the Decepticons try to decept lol.
Now this situation can happen at any point in Cars from the Old Republic to the New Republic so it's really a case of pick your era but characters reacting to Transformers is always fun.