Did you ever get this problem resolved? Inquiring minds need to know.
It's better. But it will still overheat idling slow after running all out. Will also overheat at courtesy dock if allowed to run for five or minutes.
Yamaha 60TLRZ Idling after a Duck Hunt - YouTube
Yamaha 60TLRZ Running on Muffs - YouTube
Before and after vids. I dropped the lower unit again and cinched a zip tie around the rubber water tube grommet to help keep it snugged down right to the top of the water pump housing. Maybe it will work.
Temp gun never showed any temp over 130F anywhere but in one single spot on exhaust plate.