Mazda Millenia overheating

My 1998 Millenia with 130M miles overheats. The needle rises close to hot then falls back to normal or slightly below. Hitting the A/C button can restore the temp. Fluid loss is minimal. The diagnosis is the head gasket and the oil is not impacted.

My questions are - since this appears to be a small leak, is there an additive fix?

What will likely happen next - will it definitely get worse?

Since it is overdue for a timing belt (and water pump) is this an opportune time to do the headgasket?

This car has been extremely good to me and I would like to get a couple of more years out of it. Daughter is off to college next year and now is not the time to buy a new car.

If it were an external leak, a stop-leak product might work. But it’s an internal leak where hot combustion gasses are entering the cooling system. And I don’t know of any stop-leak products that are able to withstand those temperatures.

You need to fix this because it’s not going to get any better. And continuous overheating of the engine can cause more costly damage to the engine. So have the head gasket replaced when the timing belt/water pump are replaced. Because the timing belt needs to come off when replacing the head gasket anyway. And do it soon!