2016 15HP Merc Tiller Throttle sticking after engine is warm

[jtaormino]

I have a 2016 Mercury 15hp, with tiller steer; shifter and throttle in the twist handle. The twist handle will tend to stick, and get very tight after the motor has been run for a while. It works fine when the engine is cool. I have lubricated the shift linkage with silicone under the cowl, but it gets hard to twist again after the engine has warmed up. It's not the tensioner, it's in the linkage.

I think the issue is in the shift linkage, but everything, including the cables, look OK.
Any ideas ?
Thanks