My first HD repair bill. Got screwed. Few questions? Thoughts suggestions?

So my 2018 Harley sportster 1200 48 special. About 4050 miles. I’ve only put on about 100. Just getting into motorcycle riding. Sounds like I got screwed pretty good. I’ve had it for about 6 months. Bought it out of state as a pre owned used bike. Love the bike to death. Anyways...So about a week ago I noticed my bike leaking some kind of fluid. Fast forward to today. Took it into my HD dealership here and here’s my problems.So apparently the oil bag/bladder was overfilled. Weird because I’ve never added oil to it the 6 months I’ve owned it. But somehow it has increased. Btw keep in mind never had this issue before in all 6 months. Sort of strange right? I live in AZ so I don’t know if that has anything to do with it. They need to order new parts and replace the oil bag and some other stuff inside that area to make it right.Here’s the worst news. Apparently there’s no tuner on my bike. According to the HD mechanic he said that was a huge no no. Like almost a kiss of death to my motorcycle engine. Certainly hope we’ve caught this before major serious damage occurred.Probably a massive newbie question but really in its most simplest of forms what is a tuner? Why do I need it?Is it going to change my bike? Because one of the big reasons I’ve bought this bike was because the performance and the sound of the bike when it starts up and drives off. She’s definitely a lot louder than most sportsters. I’m convinced the previous owner put some custom exhaust or something because it sounds like a soft tail instead of a sportster. Basically my fear is this tuner is going to change the things or make it sound or act different than originally.The HD guy also suggested I call back my old HD and talk to them. I’m getting the feeling of like this is something I should bring up. Because what it seems like is I bought a motorcycle and a huge piece of the motorcycle wasn’t properly attached or done right. Keep in mind this was NOT on the service history form when I got this bike. Basically whoever the owner was before me got his/her service done at the same HD out of state. HD guy said maybe they can pay for it but it’s a long shot. I mean they sold me a bike without a tuner and according to the mechanic here apparently not only is that a big no no but that’s like something you can’t miss. Like almost so far of saying it’ll be pretty hard to miss something like that. Sold it to me without letting me know? Sounds a little spineless to me.They might not do anything because I also did buy it as is. But it’s like again you would of thought the dealership would of told me about something so obvious ESPECIALLY when it can cause some serious issues without it.Definitely not feeling very good.Total cost is just over a 1000.Any thoughts? Tips? Suggestions?Thanks y’all. via /r/motorcycles https://www.reddit.com/r/motorcycles/comments/g1i62v/my_first_hd_repair_bill_got_screwed_few_questions/?utm_source=ifttt