Villiager heating problem - need help

I have 1998 Mercurry Villager and now it is winter
it takes a longtime to warm up. No warm air comes out of the vents until I start driving for a prolonged period. As soon as I stop, vents start blowing cold air. Same issue with the rear heater. Also sometimes the car has Water Coolant smell once van is driven with the heater on for a longtime.
Otherwise the car is normal and does not over heat.

Took it to a mechanic. The car was very low on
Coolant water. He did the pressure test. It was normal. But he noticed a leak coming from
the rubber hose on the intake manifold side.

He said this is a big job and it cost a lot since it is not
easy to get into lower rubber hose on the intake and
would need to remove lots of stuff and replace
the manifold gasket.

Does this make sense? Is there a way to replace
the intake rubber hose without changing the manifold gasket?