Tranny Problem?

I just got a 1970 Bug its got an IRS Tranny the problem is when I bought it the guy who I have known for a long time said that the transmission was only a couple weeks old and that it only had about 1500 miles on it. Now the problem is it will not go into first gear reverse, second, third & fourth work great but it will not go into first at all its like something is blocking the shifter from even going in that direction anyone have any clue what this could be? any help is appreciated thanks.

The car will not go into first if ur going faster than 25 miles an hr. come to a complete stop and then put it into first. Sometimes u might me pushing it too hard to the left so just try putting it straight foward instead of left foward. There is a plate under the shifter that might need to be replaced. Tell me if i've helped.