Help w/ unusual home structure

I have a quadlevel home. Floors and ceilings are 12-inch wide concrete panels. Furnace does not send heat to bedrooms, bathrooms. I have duct work in basement level and in the crawIspace but have been told that the builder also (?) tried to have the heat run through the voids in the concrete panels. I have short (3 inches high) heat registers that run the length of a wall that are not even lukewarm to the touch when the furnace is on (furnace is 1 year old -- a Rheem). I have spoken to many HVAC pros; none has been able to come up with a solution. Several years ago a contractor suggested adding a fan to the system to push heat to the bedrooms but wasn't confident it would do the job. Two years ago I installed Cozy wall furnaces in each bedroom. I am now trying to sell the home and had a potential buyer. The buyer's inspector told the buyer that my heating system was inefficient and told me I may need to replace the heat vents because they appear to be painted or rusted shut. He also said perhaps the damper in the crawlspace needs to be looked at. Because of his report, the buyer backed out of the sale. Even if the registers were rusted or painted shut (many of them appear to me open), wouldn't they be warm to the touch if heated air was passing through? I desperately need to sell my home and will do what it would reasonably take to have the problem solved, but I don't have confidence that anyone has a solution. Please HELP!