2019 3.3T: Hard brake pedal/won't start easily: Repair advice please.

[Flycaster]

I know that this has been discussed years earlier, but I need some advice on where to go to handle the following issue: After standing a day or two, brake pedal is very hard to depress and car doesn't start, initially. However, the car eventually will start after applying extreme pressure on the brake pedal, and once started there are absolutely no problems with the brakes...smooth brake depression and stopping normally. But, if the car isn't used for couple of days, then the hard brake pedal/starting issue is back. This has been going on for about 6 months. I have extensively AI'd this issue and firmly believe that because everything is normal, except for the tough start, that the problem is caused by brake booster pressure leaks from the hoses, their connections, or the check valve. Because, once the car starts and brake function is quite normal (as is the electrical system...radio, lights, etc), AI is very strongly pointing at the check valve as the culprit and not the booster brake drum (which is a high dollar item). Although, I know that AI can make mistakes, given the car's consistent normal brake performance, I believe that AI is correct in its diagnosis. So, what's my problem?

Where do I take the car for repair; be it an indy or Genesis? Being so sure about check valve replacement correcting the issue, the fix seems rather straight forward and simple (my DIY days are over as replacing the valve is not difficult and the valve is reasonably priced), but I am fearful of being ripped off. The indys I spoke to all talk about a lot of diagnosis and replacement of the Booster itself, whereas I feel, given the info I have researched and the overall normal brake performance, that the repair should entail checking for hose/connection leaks and then, if needs be, replace the check valve. Of course, if this doesn't work, then they can go further. Would like to hear your thoughts on how I should proceed. Thanks.