It appears that you've figured out the Y-pipe issue and that it's completely unrelated to the transmission problem.
@VAGfan lays out a course of repair to try on your transmission in post #482 above. I just bought my 13th Macan (a 2018 GTS) in the past 14 months (I have a dealer's license for my law firm and like to swap cars a lot), and it started exhibiting the same transmission symptoms you describe in post #489 (minus the coolant leak issue). So, I am going to attempt
@VAGfan 's recommended fix. I will report back on how it went, and if the problem is resolved, will do a DIY thread on that repair.
Since you found the thread on the Y-pipe coolant leak, I assume that was resolved with minimal issues. Did you get your issue transmission issue resolved? If yes, can you post an update?
What I have found with the first gen Macan is that there are 4 recurring maintenance problems:
-The aforementioned Y-pipe coolant leak under the intake manifold. What was a $2,000 repair has now been reduced to about a $400 repair by a shop or a $100 DIY and is a permanent fix (rather than using a thin plastic pipe that will probably break again in 6 or 7 years). It's cheap & easy enough that frankly, people should do it proactively since it will strand you. Of the 13 Macans I have had, 2 experienced this problem during my brief ownership.
-The Transfer Case. What was a $5,000+ repair has now been reduced to about a $1,350 repair. You must understand that Macan transfer cases don't break - the friction plates inside (think "clutch plates) begin to wear out, causing a slipping feeling. You can buy reman transfer cases on eBay for $800, and they come with a 2-year warranty (same as the Porsche remans). Those are Porsche trasfer cases, just not rebuilt by Porsche. Transfer case fluid and a drive shaft clamp are about $50. I pay my indie mechanic $500 for labor. Total out the door is $1,350. Of the 13 Macans I've had, 4 have needed transfer case replacement. This one could easily be a DIY, but getting the driveshaft off the transfer case output shaft is apparently tricky (so says my mechanic), so I just let him do the job for me. It can't be that bad, though, since he seems happy every time he gets to do that job.
-Timing Chain cover oil leaks. What was a $10,000+ repair has now been reduced to $20 in parts and 2 hours of labor with the "2-bolt fix." I have just done the labor myself - it's a little tricky, but not bad once you have done it once and have the small format tools you need to work in a tight space. I have heard people say "well, my mechanic says that 2-bolt fix might not solve the problem," to which I say "OK, give me the name of the person that you know who had the 2-bolt fix done and it didn't work." There's never an actual person - they've just heard it might not work. I have had to do this on 3 of the 13 Macans I've briefly owned.
-The Mechantronic valve body failure. Lucky #13 Macan for me is the first one I've had with this problem. I'm going to try the repair/rebuild that
@VAGfan describes. As I said above, I'll report back with results.
Other than these issues, the Macan appears to be very reliable. With any out of warranty European vehicle, you need to adopt an "I am the warranty" attitude and be willing to research, do some basic wrenching yourself and have a good indie mechanic for the tougher stuff (or things you don't have time to do yourself). These forums go a long way toward making that achievable. Access to a lift is helpful, too.