Have you tried to flush it?I would pull the heater control valve out and make sure it is not plugged.
Make sure the heater control valve is opening.
I think you can make it work again without replacing it. If you need to replace it the only way to do it easly is to remove the dash,and that is why the shops want so much,and there is no assurance it will not squeek.
I have taken my dash out a few times for different reasons and it is pretty easy and only takes about an hour now.
Marry the right person it will determine 95 percent of your happiness or misery. Remember that old saying,you can be right or you can be happy,I choose happy.
89 xj in progress D44,4"x 2" lift
72 Restored chevy truck 4x4,lockers,built 350,approx 400 hp.