Since you said that you have had problems opening the trunk unlocked, I think I know what is wrong. I had this problem on my '73 450 SLC. What happened was the latch in the lock had worn to a point where pushing the button would not release the trunk's latch. I got the trunk open (I honestly do not remember how, that happened 20 years ago) and removed the lock mechanism. I drilled a hole in the latch, placed a screw in in the latch, and the lock would now contact and the trunk would open.