Head Gasket Issue ?

I was reading a lot of the issues about the intake gasket & Head Gasket issues, I have a Montana ´98 and every time that is warm (210 F degrees) or every time that it is started I can see white smog on the muffle, My mechanic told that the head gasket I need to replaced, The coolant level is Ok, but sometimes I need to add an oil because the level is low. These could be related to these issues ?
Please Help
Tks.

You need to get the intake gasket replaced immediately!! Your oil is leaking internally into your coolant. This will cause a brown sludgey peanut buttery substance to clog up your radiator. If the coolant is leaking into your oil (internally), it will ruin the bearings in your motor, resulting in replacement of the entire engine. The repair can be done for aroud $400 US at an independant shop, and this will also include coolant flush. Its insignificant compared to $4K for a new motor. This is VERY COMMON with these vans, so chances are its your turn to get it replaced. Don't wait on this, the longer you let it go, the worse the potential damage to your motor will be.