First of all, congratulations on making it to (or about to reach) 200,000 miles. As for the coolant loss issue, I had a similar problem with my '02 Impala. It was the Lower Intake gaskets leaking, and I *think* the leaking started very insidiously at around 75,000 miles. At 104,000, I finally got around to replacing the gaskets. Now, with almost 205,000 miles on the vehicle, it's starting to lose coolant again. This time, I'll probably replace *both* the head and lower intake gaskets.
More than likely, this is your problem. When you replaced the intake, what gasket set did you use for the replacement? I used the metal-backed Felpros. When I did my replacement, GM had already issued "re-designed" intake gaskets, but when I went to look at them at the dealer, I wasn't impressed: looked like the same thing to me! Just couldn't feel good about putting those in there.
You know - you might want to first verify those LIM bolts are torqued down properly. On my engine, they're really l-o-n-g and narrow bolts installed with very low torque. Maybe they're not installed properly. Also, unlike the head bolts, I don't recall them being "torque-to-yield" bolts, so I re-used mine, but maybe you might want to try installing new bolts while you check the torque on them? And double-check that valley seal connecting the two sides. Maybe not enough sealant there?
2011 Equinox 1LT (new Jan 2011): Summit White / 3.0 L V6 / FWD / Pioneer Stereo / 18" Wheels / 138.2k miles [05-NOV-2019]
2002 Impala 1LT (new Jun 2002): Summit White / 3.4 L V6 / FWD / Cassette-CD Combo /225.5k miles [05-NOV-2019]