Intermitten clutch problem

Clutch changed by previous owner at 172,000. One drive axle was also changed.

Shop, a well recommended transmission specialist, cannot replicate the issue to diagnose.

Every few hundred miles, there is a severe slippage that can happen at any operating temperature. Sometimes while cruising, more often when shifting, and can happen in any gear. Sometimes need to shift to a different gear to make forward progress.

No issues found with the fluid or level, or anything else under the car.

The other issue I see is a lot of moisture coming put of the front defroster vent on a humid night. Air find compressor was done at 182,000. I do not smell or see anything that looks like antifreeze and the motor oil is a nice light brown color. I also see the condensation on the A/C hoses under the hood.

The car is otherwise in good shape. What options do I have, especially with the clutch issue? Is the defrost issue just a local problem? If something like a head gasket is suspect, I would be much less likely to get into the clutch.