Many thanks for the advice so far. Smell? Unfortunately, I discarded the fluid. I am going to start with a trial run over the weekend to determine whether the "bad" transmission is running hot. Easy test. If not running hot, I will move on to the other possible causes. If running hot, I will change out the cooler. The boat came with five brand new spares. I will post the results.
Bacchus, I thought as you did that 30 hours was surprisingly short for brown fluid even if the discs were slipping especially because I experienced no operational anomalies in 1,200 miles of cruising.
Ski, I will check for water intrusion (teaspoon method) and my run this weekend if the temp test shows normal. If water is present, I will change out the cooler as I believe this would be the likely source. However, it may take may than a couple of hours of run time to get an indication of water. I may have to run the boat until the fluid turns brown again and send a sample out for testing. Silly me, I should have retained some for a test.