only happen in cold weather, no leak in summer time, head gasket already changed long time ago, not sure still worth to fix, or just keep adding new coolant until it dies, any suggestion? Thanks in advance!

Any visible coolant anywhere on the engine or on the ground?

only happen in cold weather, no leak in summer time, head gasket already changed long time ago, not sure still worth to fix, or just keep adding new coolant until it dies, any suggestion? Thanks in advance!
Pressure test radiator,check radiator cap carefully such as rubber cracking under cap or overlapping of gasket material. This will get you going in the right direction.

only little on the ground.

Any visible coolant anywhere on the engine or on the ground?

I'd start by tracking where the dripping coolant is coming from. Can you park in a protected area (i.e. a garage) where you can spread paper under the van, to accurately find the drip location?

Can you look up under the van and see engine coolant drips still hanging on something?

Let us know what you learn.